Java反射机制概述
- 前言
- 一、Java反射机制概述
- 1. Java Reflection
- 2. 动态语言 vs 静态语言
- 二、 Class类的理解
- 1. 类的加载过程
- 1.1 初步了解
- 1.2 类的加载过程图解
- 1.3 了解：什么时候会发生类初始化？
- 1.4 类加载器的作用
- 1.5 JVM中不同类型的类的加载器
- 1.6 代码演示
- 2. 何为Class类？
- 3. Class类的常用方法方法
- 3. 哪些类型可以有Class对象？
- 三、获取Class类实例的四种方法
- 1. 调用运行时类的属性：.class
- 2. 通过运行时类的对象,调用getClass()
- 3.调用Class的静态方法：forName(String classPath)
- 4. 使用类的加载器：ClassLoader
- 5. 代码演示
- 四、 创建运行时类的对象
- 1. 引入
- 2. 语法步骤
- 3. 代码演示
- 4. 体会反射的动态性
- 五、获取运行时类的完整结构
- 1. 获取当前运行时类的属性结构
- 2. 获取当前运行时类的方法结构
- 3. 获取当前运行时类的构造器结构
- 六、调用运行时类的指定结构
- 1. 调用运行时类中指定的属性
- 2. 调用运行时类中的指定的方法
- 3. 调用运行时类中的指定的构造器
前言
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一、Java反射机制概述
1. Java Reflection
（1）Reflection（反射）是被视为动态语言的关键，反射机制允许程序在执行期 借助于ReflectionAPI取得任何类的内部信息，并能直接操作任意对象的内 部属性及方法。
（2）加载完类之后，在堆内存的方法区中就产生了一个Class类型的对象（一个类只有一个Class对象），这个对象就包含了完整的类的结构信息。我们可以通过这个对象看到类的结构。这个对象就像一面镜子，透过这个镜子看到类的结构，所以，我们形象的称之为：反射。
2. 动态语言 vs 静态语言
（1）动态语言
是一类在运行时可以改变其结构的语言：例如新的函数、对象、甚至代码可以 被引进，已有的函数可以被删除或是其他结构上的变化。通俗点说就是在运行时代码可以根据某些条件改变自身结构。
主要动态语言：Object-C、C#、JavaScript、PHP、Python、Erlang。
（2）静态语言
与动态语言相对应的，运行时结构不可变的语言就是静态语言。如Java、C、C++。Java不是动态语言，但Java可以称之为“准动态语言”。即Java有一定的动态性，我们可以利用反射机制、字节码操作获得类似动态语言的特性。 Java的动态性让编程的时候更加灵活！
（3）Java反射机制研究及应用
? Java反射机制提供的功能
- 在运行时判断任意一个对象所属的类
- 在运行时构造任意一个类的对象
- 在运行时判断任意一个类所具有的成员变量和方法
- 在运行时获取泛型信息 在运行时调用任意一个对象的成员变量和方法
- 在运行时处理注解 生成动态代理
? 反射相关的主要API
- java.lang.Class:代表一个类
- java.lang.reflect.Method:代表类的方法
- java.lang.reflect.Field:代表类的成员变量
- java.lang.reflect.Constructor:代表类的构造器 ? … …
二、 Class类的理解
1. 类的加载过程
? 程序经过
javac.exe命令以后，会生成一个或多个字节码文件(.class结尾)。
接着我们使用java.exe命令对某个字节码文件进行解释运行。相当于将某个字节码文件加载到内存中。此过程就称为类的加载。加载到内存中的类，我们就称为运行时类，此运行时类，就作为Class的一个实例。
? 换句话说，
Class的实例就对应着一个运行时类。
? 加载到内存中的运行时类，会缓存一定的时间。在此时间之内，我们可以通过不同的方式来获取此运行时类。
当程序主动使用某个类时，如果该类还未被加载到内存中，则系统会通过如下三个步骤来对该类进行初始化。
? 类的加载：将
class文件字节码内容加载到内存中，并将这些静态数据转换成方法区的运行时数据结构，然后生成一个代表这个类的java.lang.Class对象，作为方法区中类数据的访问入口（即引用地址）。所有需要访问和使用类数据只能通过这个Class对象。这个加载的过程需要类加载器参与。
? 类的链接：将Java类的二进制代码合并到JVM的运行状态之中的过程。
● 验证：确保加载的类信息符合JVM规范，例如：以cafe开头，没有安全方面的问题
● 准备：正式为类变量（static）分配内存并设置类变量默认初始值的阶段，这些内存 都将在方法区中进行分配。
● 解析：虚拟机常量池内的符号引用（常量名）替换为直接引用（地址）的过程。
? 类的初始化：
● 执行类构造器【clinit】()方法的过程。类构造器【clinit】()方法是由编译期自动收集类中 所有类变量的赋值动作和静态代码块中的语句合并产生的。（类构造器是构造类信 息的，不是构造该类对象的构造器）。
● 当初始化一个类的时候，如果发现其父类还没有进行初始化，则需要先触发其父类 的初始化。
● 虚拟机会保证一个类的()方法在多线程环境中被正确加锁和同步。
<span style="color:#000000"><span style="background-color:#282a36"><span style="color:pink"><code class="language-java"><span style="color:#ff79c6">public</span> <span style="color:#ff79c6">class</span> ClassLoadingTest <span style="color:#999999">{</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">static</span> <span style="color:#ff79c6">void</span> <span style="color:#8be9fd">main</span><span style="color:#999999">(</span>String<span style="color:#999999">[</span><span style="color:#999999">]</span> args<span style="color:#999999">)</span> <span style="color:#999999">{</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>A<span style="color:#999999">.</span>m<span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span> <span style="color:#999999">}</span>
<span style="color:#ff79c6">class</span> A <span style="color:#999999">{</span>
<span style="color:#ff79c6">static</span> <span style="color:#999999">{</span> m <span style="color:#6272a4">=</span> <span style="color:#f1fa8c">300</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#ff79c6">static</span> <span style="color:#ff79c6">int</span> m <span style="color:#6272a4">=</span> <span style="color:#f1fa8c">100</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#6272a4">//第二步：链接结束后m=0</span>
<span style="color:#6272a4">//第三步：初始化后，m的值由<clinit>()方法执行决定</span>
<span style="color:#6272a4">// 这个A的类构造器<clinit>()方法由类变量的赋值和静态代码块中的语句按照顺序合并产生，类似于</span>
<span style="color:#6272a4">// <clinit>(){</span>
<span style="color:#6272a4">// m = 300;</span>
<span style="color:#6272a4">// m = 100;</span>
<span style="color:#6272a4">// }</span>
</code></span></span></span>? 类的主动引用（一定会发生类的初始化）
- 当虚拟机启动，先初始化
main方法所在的类new一个类的对象- 调用类的静态成员（除了final常量）和静态方法
- 使用
java.lang.reflect包的方法对类进行反射调用- 当初始化一个类，如果其父类没有被初始化，则先会初始化它的父类
? 类的被动引用（不会发生类的初始化）
- 当访问一个静态域时，只有真正声明这个域的类才会被初始化
- 当通过子类引用父类的静态变量，不会导致子类初始化
- 通过数组定义类引用，不会触发此类的初始化
- 引用常量不会触发此类的初始化（常量在链接阶段就存入调用类的常量池中了）
? 类加载的作用：将class文件字节码内容加载到内存中，并将这些静态数据转换成方法区的运行时数据结构，然后在堆中生成一个代表这个类的java.lang.Class对象，作为 方法区中类数据的访问入口。
? 类缓存：标准的JavaSE类加载器可以按要求查找类，但一旦某个类被加载到类加载器 中，它将维持加载（缓存）一段时间。不过JVM垃圾回收机制可以回收这些Class对象。
? 不同类型的类的加载器：
<span style="color:#000000"><span style="background-color:#282a36"><span style="color:pink"><code class="language-java"> <span style="color:#999999">@Test</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">void</span> <span style="color:#8be9fd">test1</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">{</span>
<span style="color:#6272a4">//对于自定义类，使用系统类加载器进行加载</span>
ClassLoader classLoader <span style="color:#6272a4">=</span> ClassLoaderTest<span style="color:#999999">.</span><span style="color:#ff79c6">class</span><span style="color:#999999">.</span><span style="color:#8be9fd">getClassLoader</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>classLoader<span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#6272a4">//sun.misc.Launcher$AppClassLoader@18b4aac2:系统类加载器</span>
<span style="color:#6272a4">//调用系统类加载器的getParent()：获取扩展类加载器</span>
ClassLoader classLoader1 <span style="color:#6272a4">=</span> classLoader<span style="color:#999999">.</span><span style="color:#8be9fd">getParent</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>classLoader1<span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#6272a4">//sun.misc.Launcher$ExtClassLoader@279f2327：扩展类加载器</span>
<span style="color:#6272a4">//调用扩展类加载器的getParent()：无法获取引导类加载器</span>
<span style="color:#6272a4">//引导类加载器主要负责加载java的核心类库，无法加载自定义类的。</span>
ClassLoader classLoader2 <span style="color:#6272a4">=</span> classLoader1<span style="color:#999999">.</span><span style="color:#8be9fd">getParent</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>classLoader2<span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#6272a4">//null</span>
ClassLoader classLoader3 <span style="color:#6272a4">=</span> String<span style="color:#999999">.</span><span style="color:#ff79c6">class</span><span style="color:#999999">.</span><span style="color:#8be9fd">getClassLoader</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>classLoader3<span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#6272a4">//null</span>
<span style="color:#999999">}</span>
</code></span></span></span>? 使用系统类加载器读取
Properties配置文件。
<span style="color:#000000"><span style="background-color:#282a36"><span style="color:pink"><code class="language-java"> <span style="color:#6272a4">/*
Properties：用来读取配置文件。
*/</span>
<span style="color:#999999">@Test</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">void</span> <span style="color:#8be9fd">test2</span><span style="color:#999999">(</span><span style="color:#999999">)</span> <span style="color:#ff79c6">throws</span> Exception <span style="color:#999999">{</span>
Properties pros <span style="color:#6272a4">=</span> <span style="color:#ff79c6">new</span> Properties<span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#6272a4">//此时的文件默认在当前的module下。</span>
<span style="color:#6272a4">//读取配置文件的方式一：</span>
<span style="color:#6272a4">// FileInputStream fis = new FileInputStream("jdbc.properties");</span>
<span style="color:#6272a4">// FileInputStream fis = new FileInputStream("src\\jdbc1.properties");</span>
<span style="color:#6272a4">// pros.load(fis);</span>
<span style="color:#6272a4">//读取配置文件的方式二：使用ClassLoader</span>
<span style="color:#6272a4">//配置文件默认识别为：当前module的src下</span>
ClassLoader classLoader <span style="color:#6272a4">=</span> ClassLoaderTest<span style="color:#999999">.</span><span style="color:#ff79c6">class</span><span style="color:#999999">.</span><span style="color:#8be9fd">getClassLoader</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
InputStream is <span style="color:#6272a4">=</span> classLoader<span style="color:#999999">.</span><span style="color:#8be9fd">getResourceAsStream</span><span style="color:#999999">(</span><span style="color:#f1fa8c">"jdbc1.properties"</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
pros<span style="color:#999999">.</span><span style="color:#8be9fd">load</span><span style="color:#999999">(</span>is<span style="color:#999999">)</span><span style="color:#999999">;</span>
String user <span style="color:#6272a4">=</span> pros<span style="color:#999999">.</span><span style="color:#8be9fd">getProperty</span><span style="color:#999999">(</span><span style="color:#f1fa8c">"user"</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
String password <span style="color:#6272a4">=</span> pros<span style="color:#999999">.</span><span style="color:#8be9fd">getProperty</span><span style="color:#999999">(</span><span style="color:#f1fa8c">"password"</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span><span style="color:#f1fa8c">"user = "</span> <span style="color:#6272a4">+</span> user <span style="color:#6272a4">+</span> <span style="color:#f1fa8c">",password = "</span> <span style="color:#6272a4">+</span> password<span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#999999">}</span>
</code></span></span></span>2. 何为Class类？
?
Class类在Object类中定义了以下的方法，此方法将被所有子类继承：
<span style="color:#000000"><span style="background-color:#282a36"><span style="color:pink"><code class="language-java"><span style="color:#ff79c6">public</span> <span style="color:#ff79c6">final</span> Class <span style="color:#8be9fd">getClass</span><span style="color:#999999">(</span><span style="color:#999999">)</span>
</code></span></span></span>以上的方法返回值的类型是一个
Class类，此类是Java反射的源头，实际上所谓反射从程序的运行结果来看也很好理解，即：可以通过对象反射求出类的名称。
? 对象照镜子后可以得到的信息：某个类的属性、方法和构造器、某个类到底实现了哪些接口。对于每个类而言，
JRE都为其保留一个不变的Class类型的对象。
一个Class对象包含了特定某个结构(class/interface/enum/annotation/primitivetype/void/[])的有关信息。
?
Class本身也是一个类
?
Class对象只能由系统建立对象
? 一个加载的类在
JVM中只会有一个Class实例
? 一个Class对象对应的是一个加载到
JVM中的一个.class文件
? 每个类的实例都会记得自己是由哪个
Class实例所生成
? 通过
Class可以完整地得到一个类中的所有被加载的结构
?
Class类是Reflection的根源，针对任何你想动态加载、运行的类，唯有先获得相应的
3. Class类的常用方法方法
| 方法名 | 功能说明 |
|---|---|
static Class forName(String name) | 返回指定类名 name 的 Class 对象 |
Object newInstance() | 调用缺省构造函数，返回该Class对象的一个实例 |
getName() | 返回此Class对象所表示的实体（类、接口、数组类、基本类型或void）名称 |
Class getSuperClass() | 返回当前Class对象的父类的Class对象 |
Class [] getInterfaces() | 获取当前Class对象的接口 |
ClassLoader getClassLoader() | 返回该类的类加载器 |
Class getSuperclass() | 返回表示此Class所表示的实体的超类的Class |
Constructor[] getConstructors() | 返回一个包含某些Constructor对象的数组 |
Field[] getDeclaredFields() | 返回Field对象的一个数组 |
Method getMethod(String name,Class … paramTypes) | 返回一个Method对象，此对象的形参类型为paramType |
3. 哪些类型可以有Class对象？
（1）class： 外部类，成员(成员内部类，静态内部类)，局部内部类，匿名内部类
（2）interface：接口
（3）[]：数组
（4）enum：枚举
（5）annotation：注解@interface
（6）primitive type：基本数据类型
（7）void
三、获取Class类实例的四种方法
1. 调用运行时类的属性：.class
前提：若已知具体的类，通过类的class属性获取，该方法最为安全可靠， 程序性能最高
示例：Class clazz1 = String.class;
2. 通过运行时类的对象,调用getClass()
前提：已知某个类的实例，调用该实例的
getClass()方法获取Class对象
示例：Class clazz = “www.atguigu.com”.getClass();
3.调用Class的静态方法：forName(String classPath)
前提：已知一个类的全类名，且该类在类路径下，可通过
Class类的静态方法forName()获取，可能抛出ClassNotFoundException
示例：Class clazz = Class.forName(“java.lang.String”);
4. 使用类的加载器：ClassLoader
示例：
ClassLoader cl = this.getClass().getClassLoader();Class clazz4 = cl.loadClass(“类的全类名”);
5. 代码演示
<span style="color:#000000"><span style="background-color:#282a36"><span style="color:pink"><code class="language-java"><span style="color:#999999">@Test</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">void</span> <span style="color:#8be9fd">test1</span><span style="color:#999999">(</span><span style="color:#999999">)</span> <span style="color:#ff79c6">throws</span> ClassNotFoundException <span style="color:#999999">{</span>
<span style="color:#6272a4">//方式一：调用运行时类的属性：.class</span>
Class clazz1 <span style="color:#6272a4">=</span> Person<span style="color:#999999">.</span><span style="color:#ff79c6">class</span><span style="color:#999999">;</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>clazz1<span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#6272a4">//class com.jiaying.java1.Person</span>
<span style="color:#6272a4">//方式二：通过运行时类的对象,调用getClass()</span>
Person p1 <span style="color:#6272a4">=</span> <span style="color:#ff79c6">new</span> Person<span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
Class clazz2 <span style="color:#6272a4">=</span> p1<span style="color:#999999">.</span><span style="color:#8be9fd">getClass</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>clazz2<span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#6272a4">//class com.jiaying.java1.Person</span>
<span style="color:#6272a4">//方式三：调用Class的静态方法：forName(String classPath)</span>
Class clazz3 <span style="color:#6272a4">=</span> Class<span style="color:#999999">.</span><span style="color:#8be9fd">forName</span><span style="color:#999999">(</span><span style="color:#f1fa8c">"com.jiaying.java1.Person"</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
Class clazz5 <span style="color:#6272a4">=</span> Class<span style="color:#999999">.</span><span style="color:#8be9fd">forName</span><span style="color:#999999">(</span><span style="color:#f1fa8c">"java.lang.String"</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>clazz3<span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#6272a4">//class com.jiaying.java1.Person</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>clazz5<span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#6272a4">//class java.lang.String</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>clazz1 <span style="color:#6272a4">==</span> clazz2<span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#6272a4">//true</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>clazz1 <span style="color:#6272a4">==</span> clazz3<span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#6272a4">//true</span>
<span style="color:#6272a4">//方式四：使用类的加载器：ClassLoader (了解)</span>
ClassLoader classLoader <span style="color:#6272a4">=</span> ReflectionTest<span style="color:#999999">.</span><span style="color:#ff79c6">class</span><span style="color:#999999">.</span><span style="color:#8be9fd">getClassLoader</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
Class clazz4 <span style="color:#6272a4">=</span> classLoader<span style="color:#999999">.</span><span style="color:#8be9fd">loadClass</span><span style="color:#999999">(</span><span style="color:#f1fa8c">"com.jiaying.java1.Person"</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>clazz4<span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#6272a4">//class com.jiaying.java1.Person</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>clazz1 <span style="color:#6272a4">==</span> clazz4<span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#6272a4">//true</span>
<span style="color:#999999">}</span>
</code></span></span></span>四、 创建运行时类的对象
1. 引入
? 有了Class对象，能做什么？
创建类的对象：调用
Class对象的newInstance()方法
要求：
- 类必须有一个无参数的构造器。
- 类的构造器的访问权限需要足够。
? 难道没有无参的构造器就不能创建对象了吗？
不是！只要在操作的时候明确的调用类中的构造器，并将参数传递进去之后，才可以实例化操作。
步骤如下：
- 通过
Class类的getDeclaredConstructor(Class … parameterTypes)取得本类的指定形参类型的构造器- 向构造器的形参中传递一个对象数组进去，里面包含了构造器中所需的各个参数。
- 通过
Constructor实例化对象。
2. 语法步骤
（1）根据全类名获取对应的
Class对象
<span style="color:#000000"><span style="background-color:#282a36"><span style="color:pink"><code class="language-java">String name <span style="color:#6272a4">=</span> “atguigu<span style="color:#999999">.</span>java<span style="color:#999999">.</span>Person"<span style="color:#999999">;</span>
Class clazz <span style="color:#6272a4">=</span> <span style="color:#ff79c6">null</span><span style="color:#999999">;</span>
clazz <span style="color:#6272a4">=</span> Class<span style="color:#999999">.</span><span style="color:#8be9fd">forName</span><span style="color:#999999">(</span>name<span style="color:#999999">)</span><span style="color:#999999">;</span>
</code></span></span></span>（2）调用指定参数结构的构造器，生成
Constructor的实例
<span style="color:#000000"><span style="background-color:#282a36"><span style="color:pink"><code class="language-java">Constructor con <span style="color:#6272a4">=</span> clazz<span style="color:#999999">.</span><span style="color:#8be9fd">getConstructor</span><span style="color:#999999">(</span>String<span style="color:#999999">.</span><span style="color:#ff79c6">class</span><span style="color:#999999">,</span>Integer<span style="color:#999999">.</span><span style="color:#ff79c6">class</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
</code></span></span></span>（3）通过
Constructor的实例创建对应类的对象，并初始化类属性
<span style="color:#000000"><span style="background-color:#282a36"><span style="color:pink"><code class="language-java">Person p2 <span style="color:#6272a4">=</span> <span style="color:#999999">(</span>Person<span style="color:#999999">)</span> con<span style="color:#999999">.</span><span style="color:#8be9fd">newInstance</span><span style="color:#999999">(</span><span style="color:#f1fa8c">"Peter"</span><span style="color:#999999">,</span><span style="color:#f1fa8c">20</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>p2<span style="color:#999999">)</span><span style="color:#999999">;</span>
</code></span></span></span>3. 代码演示
<span style="color:#000000"><span style="background-color:#282a36"><span style="color:pink"><code class="language-java"> <span style="color:#999999">@Test</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">void</span> <span style="color:#8be9fd">test1</span><span style="color:#999999">(</span><span style="color:#999999">)</span> <span style="color:#ff79c6">throws</span> IllegalAccessException<span style="color:#999999">,</span> InstantiationException <span style="color:#999999">{</span>
Class<span style="color:#999999"><</span>Person<span style="color:#999999">></span> clazz <span style="color:#6272a4">=</span> Person<span style="color:#999999">.</span><span style="color:#ff79c6">class</span><span style="color:#999999">;</span>
<span style="color:#6272a4">/*
newInstance():调用此方法，创建对应的运行时类的对象。内部调用了运行时类的空参的构造器。
要想此方法正常的创建运行时类的对象，要求：
1.运行时类必须提供空参的构造器
2.空参的构造器的访问权限得够。通常，设置为public。
在javabean中要求提供一个public的空参构造器。原因：
1.便于通过反射，创建运行时类的对象
2.便于子类继承此运行时类时，默认调用super()时，保证父类有此构造器
*/</span>
Person obj <span style="color:#6272a4">=</span> clazz<span style="color:#999999">.</span><span style="color:#8be9fd">newInstance</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>obj<span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
</code></span></span></span>4. 体会反射的动态性
<span style="color:#000000"><span style="background-color:#282a36"><span style="color:pink"><code class="language-java"><span style="color:#6272a4">//体会反射的动态性</span>
<span style="color:#999999">@Test</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">void</span> <span style="color:#8be9fd">test2</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">{</span>
<span style="color:#ff79c6">for</span><span style="color:#999999">(</span><span style="color:#ff79c6">int</span> i <span style="color:#6272a4">=</span> <span style="color:#f1fa8c">0</span><span style="color:#999999">;</span>i <span style="color:#6272a4"><</span> <span style="color:#f1fa8c">100</span><span style="color:#999999">;</span>i<span style="color:#6272a4">++</span><span style="color:#999999">)</span><span style="color:#999999">{</span>
<span style="color:#ff79c6">int</span> num <span style="color:#6272a4">=</span> <span style="color:#ff79c6">new</span> Random<span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">.</span><span style="color:#8be9fd">nextInt</span><span style="color:#999999">(</span><span style="color:#f1fa8c">3</span><span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#6272a4">//0,1,2</span>
String classPath <span style="color:#6272a4">=</span> <span style="color:#f1fa8c">""</span><span style="color:#999999">;</span>
<span style="color:#ff79c6">switch</span><span style="color:#999999">(</span>num<span style="color:#999999">)</span><span style="color:#999999">{</span>
<span style="color:#ff79c6">case</span> <span style="color:#f1fa8c">0</span><span style="color:#6272a4">:</span>
classPath <span style="color:#6272a4">=</span> <span style="color:#f1fa8c">"java.util.Date"</span><span style="color:#999999">;</span>
<span style="color:#ff79c6">break</span><span style="color:#999999">;</span>
<span style="color:#ff79c6">case</span> <span style="color:#f1fa8c">1</span><span style="color:#6272a4">:</span>
classPath <span style="color:#6272a4">=</span> <span style="color:#f1fa8c">"java.lang.Object"</span><span style="color:#999999">;</span>
<span style="color:#ff79c6">break</span><span style="color:#999999">;</span>
<span style="color:#ff79c6">case</span> <span style="color:#f1fa8c">2</span><span style="color:#6272a4">:</span>
classPath <span style="color:#6272a4">=</span> <span style="color:#f1fa8c">"com.atguigu.java.Person"</span><span style="color:#999999">;</span>
<span style="color:#ff79c6">break</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#ff79c6">try</span> <span style="color:#999999">{</span>
Object obj <span style="color:#6272a4">=</span> <span style="color:#8be9fd">getInstance</span><span style="color:#999999">(</span>classPath<span style="color:#999999">)</span><span style="color:#999999">;</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>obj<span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span> <span style="color:#ff79c6">catch</span> <span style="color:#999999">(</span>Exception e<span style="color:#999999">)</span> <span style="color:#999999">{</span>
e<span style="color:#999999">.</span><span style="color:#8be9fd">printStackTrace</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#999999">}</span>
<span style="color:#999999">}</span>
<span style="color:#6272a4">/*
创建一个指定类的对象。
classPath:指定类的全类名
*/</span>
<span style="color:#ff79c6">public</span> Object <span style="color:#8be9fd">getInstance</span><span style="color:#999999">(</span>String classPath<span style="color:#999999">)</span> <span style="color:#ff79c6">throws</span> Exception <span style="color:#999999">{</span>
Class clazz <span style="color:#6272a4">=</span> Class<span style="color:#999999">.</span><span style="color:#8be9fd">forName</span><span style="color:#999999">(</span>classPath<span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#ff79c6">return</span> clazz<span style="color:#999999">.</span><span style="color:#8be9fd">newInstance</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#999999">}</span>
</code></span></span></span>五、获取运行时类的完整结构
提供具有丰富内容的Person类
<span style="color:#000000"><span style="background-color:#282a36"><span style="color:pink"><code class="language-java"><span style="color:#6272a4">//接口</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">interface</span> MyInterface <span style="color:#999999">{</span>
<span style="color:#ff79c6">void</span> <span style="color:#8be9fd">info</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#6272a4">//注解</span>
<span style="color:#999999">@Target</span><span style="color:#999999">(</span><span style="color:#999999">{</span>TYPE<span style="color:#999999">,</span> FIELD<span style="color:#999999">,</span> METHOD<span style="color:#999999">,</span> PARAMETER<span style="color:#999999">,</span> CONSTRUCTOR<span style="color:#999999">,</span> LOCAL_VARIABLE<span style="color:#999999">}</span><span style="color:#999999">)</span>
<span style="color:#999999">@Retention</span><span style="color:#999999">(</span>RetentionPolicy<span style="color:#999999">.</span>RUNTIME<span style="color:#999999">)</span>
<span style="color:#ff79c6">public</span> <span style="color:#999999">@interface</span> MyAnnotation <span style="color:#999999">{</span>
String <span style="color:#8be9fd">value</span><span style="color:#999999">(</span><span style="color:#999999">)</span> <span style="color:#ff79c6">default</span> <span style="color:#f1fa8c">"hello"</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#6272a4">//父类</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">class</span> Creature<span style="color:#999999"><</span>T<span style="color:#999999">></span> <span style="color:#ff79c6">implements</span> Serializable <span style="color:#999999">{</span>
<span style="color:#ff79c6">private</span> <span style="color:#ff79c6">char</span> gender<span style="color:#999999">;</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">double</span> weight<span style="color:#999999">;</span>
<span style="color:#ff79c6">private</span> <span style="color:#ff79c6">void</span> <span style="color:#8be9fd">breath</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">{</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span><span style="color:#f1fa8c">"生物呼吸"</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">void</span> <span style="color:#8be9fd">eat</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">{</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span><span style="color:#f1fa8c">"生物吃东西"</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#999999">}</span>
<span style="color:#6272a4">//Person类</span>
<span style="color:#999999">@MyAnnotation</span><span style="color:#999999">(</span>value<span style="color:#6272a4">=</span><span style="color:#f1fa8c">"hi"</span><span style="color:#999999">)</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">class</span> Person <span style="color:#ff79c6">extends</span> Creature<span style="color:#999999"><</span>String<span style="color:#999999">></span> <span style="color:#ff79c6">implements</span> Comparable<span style="color:#999999"><</span>String<span style="color:#999999">></span><span style="color:#999999">,</span>MyInterface<span style="color:#999999">{</span>
<span style="color:#ff79c6">private</span> String name<span style="color:#999999">;</span>
<span style="color:#ff79c6">int</span> age<span style="color:#999999">;</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">int</span> id<span style="color:#999999">;</span>
<span style="color:#ff79c6">public</span> Person<span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">{</span><span style="color:#999999">}</span>
<span style="color:#999999">@MyAnnotation</span><span style="color:#999999">(</span>value<span style="color:#6272a4">=</span><span style="color:#f1fa8c">"abc"</span><span style="color:#999999">)</span>
<span style="color:#ff79c6">private</span> Person<span style="color:#999999">(</span>String name<span style="color:#999999">)</span><span style="color:#999999">{</span>
<span style="color:#ff79c6">this</span><span style="color:#999999">.</span>name <span style="color:#6272a4">=</span> name<span style="color:#999999">;</span>
<span style="color:#999999">}</span>
Person<span style="color:#999999">(</span>String name<span style="color:#999999">,</span><span style="color:#ff79c6">int</span> age<span style="color:#999999">)</span><span style="color:#999999">{</span>
<span style="color:#ff79c6">this</span><span style="color:#999999">.</span>name <span style="color:#6272a4">=</span> name<span style="color:#999999">;</span>
<span style="color:#ff79c6">this</span><span style="color:#999999">.</span>age <span style="color:#6272a4">=</span> age<span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#999999">@MyAnnotation</span>
<span style="color:#ff79c6">private</span> String <span style="color:#8be9fd">show</span><span style="color:#999999">(</span>String nation<span style="color:#999999">)</span><span style="color:#999999">{</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span><span style="color:#f1fa8c">"我的国籍是："</span> <span style="color:#6272a4">+</span> nation<span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#ff79c6">return</span> nation<span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#ff79c6">public</span> String <span style="color:#8be9fd">display</span><span style="color:#999999">(</span>String interests<span style="color:#999999">,</span><span style="color:#ff79c6">int</span> age<span style="color:#999999">)</span> <span style="color:#ff79c6">throws</span> NullPointerException<span style="color:#999999">,</span>ClassCastException<span style="color:#999999">{</span>
<span style="color:#ff79c6">return</span> interests <span style="color:#6272a4">+</span> age<span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#999999">@Override</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">void</span> <span style="color:#8be9fd">info</span><span style="color:#999999">(</span><span style="color:#999999">)</span> <span style="color:#999999">{</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span><span style="color:#f1fa8c">"我是一个人"</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#999999">@Override</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">int</span> <span style="color:#8be9fd">compareTo</span><span style="color:#999999">(</span>String o<span style="color:#999999">)</span> <span style="color:#999999">{</span>
<span style="color:#ff79c6">return</span> <span style="color:#f1fa8c">0</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#ff79c6">private</span> <span style="color:#ff79c6">static</span> <span style="color:#ff79c6">void</span> <span style="color:#8be9fd">showDesc</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">{</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span><span style="color:#f1fa8c">"我是一个可爱的人"</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#999999">@Override</span>
<span style="color:#ff79c6">public</span> String <span style="color:#8be9fd">toString</span><span style="color:#999999">(</span><span style="color:#999999">)</span> <span style="color:#999999">{</span>
<span style="color:#ff79c6">return</span> <span style="color:#f1fa8c">"Person{"</span> <span style="color:#6272a4">+</span>
<span style="color:#f1fa8c">"name='"</span> <span style="color:#6272a4">+</span> name <span style="color:#6272a4">+</span> <span style="color:#f1fa8c">'\''</span> <span style="color:#6272a4">+</span>
<span style="color:#f1fa8c">", age="</span> <span style="color:#6272a4">+</span> age <span style="color:#6272a4">+</span>
<span style="color:#f1fa8c">", id="</span> <span style="color:#6272a4">+</span> id <span style="color:#6272a4">+</span>
<span style="color:#f1fa8c">'}'</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#999999">}</span>
</code></span></span></span>1. 获取当前运行时类的属性结构
| 方法 | 作用 |
|---|---|
public Field[] getFields() | 返回此Class对象所表示的类或接口的public的Field |
public Field[] getDeclaredFields() | 返回此Class对象所表示的类或接口的全部Field |
- Field方法中：
| 方法 | 作用 |
|---|---|
public int getModifiers() | 以整数形式返回此Field的修饰符 |
public Class<?> getType() | 得到Field的属性类型 |
public String getName() | 返回Field的名称 |
<span style="color:#000000"><span style="background-color:#282a36"><span style="color:pink"><code class="language-java"> <span style="color:#999999">@Test</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">void</span> <span style="color:#8be9fd">test1</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">{</span>
Class clazz <span style="color:#6272a4">=</span> Person<span style="color:#999999">.</span><span style="color:#ff79c6">class</span><span style="color:#999999">;</span>
<span style="color:#6272a4">//获取属性结构</span>
<span style="color:#6272a4">//getFields():获取当前运行时类及其父类中声明为public访问权限的属性</span>
Field<span style="color:#999999">[</span><span style="color:#999999">]</span> fields <span style="color:#6272a4">=</span> clazz<span style="color:#999999">.</span><span style="color:#8be9fd">getFields</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#ff79c6">for</span><span style="color:#999999">(</span>Field f <span style="color:#6272a4">:</span> fields<span style="color:#999999">)</span><span style="color:#999999">{</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>f<span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#6272a4">//getDeclaredFields():获取当前运行时类中声明的所有属性。（不包含父类中声明的属性）</span>
Field<span style="color:#999999">[</span><span style="color:#999999">]</span> declaredFields <span style="color:#6272a4">=</span> clazz<span style="color:#999999">.</span><span style="color:#8be9fd">getDeclaredFields</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#ff79c6">for</span><span style="color:#999999">(</span>Field f <span style="color:#6272a4">:</span> declaredFields<span style="color:#999999">)</span><span style="color:#999999">{</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>f<span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#999999">}</span>
<span style="color:#6272a4">//权限修饰符 数据类型 变量名</span>
<span style="color:#999999">@Test</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">void</span> <span style="color:#8be9fd">test2</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">{</span>
Class clazz <span style="color:#6272a4">=</span> Person<span style="color:#999999">.</span><span style="color:#ff79c6">class</span><span style="color:#999999">;</span>
Field<span style="color:#999999">[</span><span style="color:#999999">]</span> declaredFields <span style="color:#6272a4">=</span> clazz<span style="color:#999999">.</span><span style="color:#8be9fd">getDeclaredFields</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#ff79c6">for</span><span style="color:#999999">(</span>Field f <span style="color:#6272a4">:</span> declaredFields<span style="color:#999999">)</span><span style="color:#999999">{</span>
<span style="color:#6272a4">//1.权限修饰符</span>
<span style="color:#ff79c6">int</span> modifier <span style="color:#6272a4">=</span> f<span style="color:#999999">.</span><span style="color:#8be9fd">getModifiers</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">print</span><span style="color:#999999">(</span>Modifier<span style="color:#999999">.</span><span style="color:#8be9fd">toString</span><span style="color:#999999">(</span>modifier<span style="color:#999999">)</span> <span style="color:#6272a4">+</span> <span style="color:#f1fa8c">"\t"</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#6272a4">//2.数据类型</span>
Class type <span style="color:#6272a4">=</span> f<span style="color:#999999">.</span><span style="color:#8be9fd">getType</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">print</span><span style="color:#999999">(</span>type<span style="color:#999999">.</span><span style="color:#8be9fd">getName</span><span style="color:#999999">(</span><span style="color:#999999">)</span> <span style="color:#6272a4">+</span> <span style="color:#f1fa8c">"\t"</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#6272a4">//3.变量名</span>
String fName <span style="color:#6272a4">=</span> f<span style="color:#999999">.</span><span style="color:#8be9fd">getName</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">print</span><span style="color:#999999">(</span>fName<span style="color:#999999">)</span><span style="color:#999999">;</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#999999">}</span>
<span style="color:#999999">}</span>
</code></span></span></span>2. 获取当前运行时类的方法结构
| 方法 | 作用 |
|---|---|
public Method[] getMethods() | 返回此Class对象所表示的类或接口的public的方法 |
public Method[] getDeclaredMethods() | 返回此Class对象所表示的类或接口的全部方法 |
- Method类中：
| 方法 | 作用 |
|---|---|
public Class<?> getReturnType() | 取得全部的返回值 |
public Class<?>[] getParameterTypes() | 取得全部的参数 |
public int getModifiers() | 取得修饰符 |
public Class<?>[] getExceptionTypes() | 取得异常信息 |
<span style="color:#000000"><span style="background-color:#282a36"><span style="color:pink"><code class="language-java"> <span style="color:#999999">@Test</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">void</span> <span style="color:#8be9fd">test1</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">{</span>
Class clazz <span style="color:#6272a4">=</span> Person<span style="color:#999999">.</span><span style="color:#ff79c6">class</span><span style="color:#999999">;</span>
<span style="color:#6272a4">//getMethods():获取当前运行时类及其所有父类中声明为public权限的方法</span>
Method<span style="color:#999999">[</span><span style="color:#999999">]</span> methods <span style="color:#6272a4">=</span> clazz<span style="color:#999999">.</span><span style="color:#8be9fd">getMethods</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#ff79c6">for</span><span style="color:#999999">(</span>Method m <span style="color:#6272a4">:</span> methods<span style="color:#999999">)</span><span style="color:#999999">{</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>m<span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#6272a4">//getDeclaredMethods():获取当前运行时类中声明的所有方法。（不包含父类中声明的方法）</span>
Method<span style="color:#999999">[</span><span style="color:#999999">]</span> declaredMethods <span style="color:#6272a4">=</span> clazz<span style="color:#999999">.</span><span style="color:#8be9fd">getDeclaredMethods</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#ff79c6">for</span><span style="color:#999999">(</span>Method m <span style="color:#6272a4">:</span> declaredMethods<span style="color:#999999">)</span><span style="color:#999999">{</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>m<span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#999999">}</span>
<span style="color:#6272a4">/*
@Xxxx
权限修饰符 返回值类型 方法名(参数类型1 形参名1,...) throws XxxException{}
*/</span>
<span style="color:#999999">@Test</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">void</span> <span style="color:#8be9fd">test2</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">{</span>
Class clazz <span style="color:#6272a4">=</span> Person<span style="color:#999999">.</span><span style="color:#ff79c6">class</span><span style="color:#999999">;</span>
Method<span style="color:#999999">[</span><span style="color:#999999">]</span> declaredMethods <span style="color:#6272a4">=</span> clazz<span style="color:#999999">.</span><span style="color:#8be9fd">getDeclaredMethods</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#ff79c6">for</span><span style="color:#999999">(</span>Method m <span style="color:#6272a4">:</span> declaredMethods<span style="color:#999999">)</span><span style="color:#999999">{</span>
<span style="color:#6272a4">//1.获取方法声明的注解</span>
Annotation<span style="color:#999999">[</span><span style="color:#999999">]</span> annos <span style="color:#6272a4">=</span> m<span style="color:#999999">.</span><span style="color:#8be9fd">getAnnotations</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#ff79c6">for</span><span style="color:#999999">(</span>Annotation a <span style="color:#6272a4">:</span> annos<span style="color:#999999">)</span><span style="color:#999999">{</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>a<span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#6272a4">//2.权限修饰符</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">print</span><span style="color:#999999">(</span>Modifier<span style="color:#999999">.</span><span style="color:#8be9fd">toString</span><span style="color:#999999">(</span>m<span style="color:#999999">.</span><span style="color:#8be9fd">getModifiers</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">)</span> <span style="color:#6272a4">+</span> <span style="color:#f1fa8c">"\t"</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#6272a4">//3.返回值类型</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">print</span><span style="color:#999999">(</span>m<span style="color:#999999">.</span><span style="color:#8be9fd">getReturnType</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">.</span><span style="color:#8be9fd">getName</span><span style="color:#999999">(</span><span style="color:#999999">)</span> <span style="color:#6272a4">+</span> <span style="color:#f1fa8c">"\t"</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#6272a4">//4.方法名</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">print</span><span style="color:#999999">(</span>m<span style="color:#999999">.</span><span style="color:#8be9fd">getName</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">print</span><span style="color:#999999">(</span><span style="color:#f1fa8c">"("</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#6272a4">//5.形参列表</span>
Class<span style="color:#999999">[</span><span style="color:#999999">]</span> parameterTypes <span style="color:#6272a4">=</span> m<span style="color:#999999">.</span><span style="color:#8be9fd">getParameterTypes</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#ff79c6">if</span><span style="color:#999999">(</span><span style="color:#6272a4">!</span><span style="color:#999999">(</span>parameterTypes <span style="color:#6272a4">==</span> <span style="color:#ff79c6">null</span> <span style="color:#6272a4">&&</span> parameterTypes<span style="color:#999999">.</span>length <span style="color:#6272a4">==</span> <span style="color:#f1fa8c">0</span><span style="color:#999999">)</span><span style="color:#999999">)</span><span style="color:#999999">{</span>
<span style="color:#ff79c6">for</span><span style="color:#999999">(</span><span style="color:#ff79c6">int</span> i <span style="color:#6272a4">=</span> <span style="color:#f1fa8c">0</span><span style="color:#999999">;</span>i <span style="color:#6272a4"><</span> parameterTypes<span style="color:#999999">.</span>length<span style="color:#999999">;</span>i<span style="color:#6272a4">++</span><span style="color:#999999">)</span><span style="color:#999999">{</span>
<span style="color:#ff79c6">if</span><span style="color:#999999">(</span>i <span style="color:#6272a4">==</span> parameterTypes<span style="color:#999999">.</span>length <span style="color:#6272a4">-</span> <span style="color:#f1fa8c">1</span><span style="color:#999999">)</span><span style="color:#999999">{</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">print</span><span style="color:#999999">(</span>parameterTypes<span style="color:#999999">[</span>i<span style="color:#999999">]</span><span style="color:#999999">.</span><span style="color:#8be9fd">getName</span><span style="color:#999999">(</span><span style="color:#999999">)</span> <span style="color:#6272a4">+</span> <span style="color:#f1fa8c">" args_"</span> <span style="color:#6272a4">+</span> i<span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#ff79c6">break</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">print</span><span style="color:#999999">(</span>parameterTypes<span style="color:#999999">[</span>i<span style="color:#999999">]</span><span style="color:#999999">.</span><span style="color:#8be9fd">getName</span><span style="color:#999999">(</span><span style="color:#999999">)</span> <span style="color:#6272a4">+</span> <span style="color:#f1fa8c">" args_"</span> <span style="color:#6272a4">+</span> i <span style="color:#6272a4">+</span> <span style="color:#f1fa8c">","</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#999999">}</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">print</span><span style="color:#999999">(</span><span style="color:#f1fa8c">")"</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#6272a4">//6.抛出的异常</span>
Class<span style="color:#999999">[</span><span style="color:#999999">]</span> exceptionTypes <span style="color:#6272a4">=</span> m<span style="color:#999999">.</span><span style="color:#8be9fd">getExceptionTypes</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#ff79c6">if</span><span style="color:#999999">(</span>exceptionTypes<span style="color:#999999">.</span>length <span style="color:#6272a4">></span> <span style="color:#f1fa8c">0</span><span style="color:#999999">)</span><span style="color:#999999">{</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">print</span><span style="color:#999999">(</span><span style="color:#f1fa8c">"throws "</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#ff79c6">for</span><span style="color:#999999">(</span><span style="color:#ff79c6">int</span> i <span style="color:#6272a4">=</span> <span style="color:#f1fa8c">0</span><span style="color:#999999">;</span>i <span style="color:#6272a4"><</span> exceptionTypes<span style="color:#999999">.</span>length<span style="color:#999999">;</span>i<span style="color:#6272a4">++</span><span style="color:#999999">)</span><span style="color:#999999">{</span>
<span style="color:#ff79c6">if</span><span style="color:#999999">(</span>i <span style="color:#6272a4">==</span> exceptionTypes<span style="color:#999999">.</span>length <span style="color:#6272a4">-</span> <span style="color:#f1fa8c">1</span><span style="color:#999999">)</span><span style="color:#999999">{</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">print</span><span style="color:#999999">(</span>exceptionTypes<span style="color:#999999">[</span>i<span style="color:#999999">]</span><span style="color:#999999">.</span><span style="color:#8be9fd">getName</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#ff79c6">break</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">print</span><span style="color:#999999">(</span>exceptionTypes<span style="color:#999999">[</span>i<span style="color:#999999">]</span><span style="color:#999999">.</span><span style="color:#8be9fd">getName</span><span style="color:#999999">(</span><span style="color:#999999">)</span> <span style="color:#6272a4">+</span> <span style="color:#f1fa8c">","</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#999999">}</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#999999">}</span>
<span style="color:#999999">}</span>
</code></span></span></span>3. 获取当前运行时类的构造器结构
| 方法 | 作用 |
|---|---|
public Constructor<T>[] getConstructors() | 返回此 Class 对象所表示的类的所有public构造方法。 |
public Constructor<T>[] getDeclaredConstructors() | 返回此 Class 对象表示的类声明的所有构造方法。 |
- Constructor类中：
| 方法 | 作用 |
|---|---|
public int getModifiers() | 取得修饰符 |
public String getName() | 取得方法名称 |
public Class<?>[] getParameterTypes() | 取得参数的类型 |
<span style="color:#000000"><span style="background-color:#282a36"><span style="color:pink"><code class="language-java"><span style="color:#6272a4">/*
获取构造器结构
*/</span>
<span style="color:#999999">@Test</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">void</span> <span style="color:#8be9fd">test1</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">{</span>
Class clazz <span style="color:#6272a4">=</span> Person<span style="color:#999999">.</span><span style="color:#ff79c6">class</span><span style="color:#999999">;</span>
<span style="color:#6272a4">//getConstructors():获取当前运行时类中声明为public的构造器</span>
Constructor<span style="color:#999999">[</span><span style="color:#999999">]</span> constructors <span style="color:#6272a4">=</span> clazz<span style="color:#999999">.</span><span style="color:#8be9fd">getConstructors</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#ff79c6">for</span><span style="color:#999999">(</span>Constructor c <span style="color:#6272a4">:</span> constructors<span style="color:#999999">)</span><span style="color:#999999">{</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>c<span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#6272a4">//getDeclaredConstructors():获取当前运行时类中声明的所有的构造器</span>
Constructor<span style="color:#999999">[</span><span style="color:#999999">]</span> declaredConstructors <span style="color:#6272a4">=</span> clazz<span style="color:#999999">.</span><span style="color:#8be9fd">getDeclaredConstructors</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#ff79c6">for</span><span style="color:#999999">(</span>Constructor c <span style="color:#6272a4">:</span> declaredConstructors<span style="color:#999999">)</span><span style="color:#999999">{</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>c<span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#999999">}</span>
<span style="color:#6272a4">/*
获取运行时类的父类
*/</span>
<span style="color:#999999">@Test</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">void</span> <span style="color:#8be9fd">test2</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">{</span>
Class clazz <span style="color:#6272a4">=</span> Person<span style="color:#999999">.</span><span style="color:#ff79c6">class</span><span style="color:#999999">;</span>
Class superclass <span style="color:#6272a4">=</span> clazz<span style="color:#999999">.</span><span style="color:#8be9fd">getSuperclass</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>superclass<span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#6272a4">/*
获取运行时类的带泛型的父类
*/</span>
<span style="color:#999999">@Test</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">void</span> <span style="color:#8be9fd">test3</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">{</span>
Class clazz <span style="color:#6272a4">=</span> Person<span style="color:#999999">.</span><span style="color:#ff79c6">class</span><span style="color:#999999">;</span>
Type genericSuperclass <span style="color:#6272a4">=</span> clazz<span style="color:#999999">.</span><span style="color:#8be9fd">getGenericSuperclass</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>genericSuperclass<span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#6272a4">/*
获取运行时类的带泛型的父类的泛型
代码：逻辑性代码 vs 功能性代码
*/</span>
<span style="color:#999999">@Test</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">void</span> <span style="color:#8be9fd">test4</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">{</span>
Class clazz <span style="color:#6272a4">=</span> Person<span style="color:#999999">.</span><span style="color:#ff79c6">class</span><span style="color:#999999">;</span>
Type genericSuperclass <span style="color:#6272a4">=</span> clazz<span style="color:#999999">.</span><span style="color:#8be9fd">getGenericSuperclass</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
ParameterizedType paramType <span style="color:#6272a4">=</span> <span style="color:#999999">(</span>ParameterizedType<span style="color:#999999">)</span> genericSuperclass<span style="color:#999999">;</span>
<span style="color:#6272a4">//获取泛型类型</span>
Type<span style="color:#999999">[</span><span style="color:#999999">]</span> actualTypeArguments <span style="color:#6272a4">=</span> paramType<span style="color:#999999">.</span><span style="color:#8be9fd">getActualTypeArguments</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#6272a4">// System.out.println(actualTypeArguments[0].getTypeName());</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span><span style="color:#999999">(</span><span style="color:#999999">(</span>Class<span style="color:#999999">)</span>actualTypeArguments<span style="color:#999999">[</span><span style="color:#f1fa8c">0</span><span style="color:#999999">]</span><span style="color:#999999">)</span><span style="color:#999999">.</span><span style="color:#8be9fd">getName</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#6272a4">/*
获取运行时类实现的接口
*/</span>
<span style="color:#999999">@Test</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">void</span> <span style="color:#8be9fd">test5</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">{</span>
Class clazz <span style="color:#6272a4">=</span> Person<span style="color:#999999">.</span><span style="color:#ff79c6">class</span><span style="color:#999999">;</span>
Class<span style="color:#999999">[</span><span style="color:#999999">]</span> interfaces <span style="color:#6272a4">=</span> clazz<span style="color:#999999">.</span><span style="color:#8be9fd">getInterfaces</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#ff79c6">for</span><span style="color:#999999">(</span>Class c <span style="color:#6272a4">:</span> interfaces<span style="color:#999999">)</span><span style="color:#999999">{</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>c<span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#6272a4">//获取运行时类的父类实现的接口</span>
Class<span style="color:#999999">[</span><span style="color:#999999">]</span> interfaces1 <span style="color:#6272a4">=</span> clazz<span style="color:#999999">.</span><span style="color:#8be9fd">getSuperclass</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">.</span><span style="color:#8be9fd">getInterfaces</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#ff79c6">for</span><span style="color:#999999">(</span>Class c <span style="color:#6272a4">:</span> interfaces1<span style="color:#999999">)</span><span style="color:#999999">{</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>c<span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#999999">}</span>
<span style="color:#6272a4">/*
获取运行时类所在的包
*/</span>
<span style="color:#999999">@Test</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">void</span> <span style="color:#8be9fd">test6</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">{</span>
Class clazz <span style="color:#6272a4">=</span> Person<span style="color:#999999">.</span><span style="color:#ff79c6">class</span><span style="color:#999999">;</span>
Package pack <span style="color:#6272a4">=</span> clazz<span style="color:#999999">.</span><span style="color:#8be9fd">getPackage</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>pack<span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#6272a4">/*
获取运行时类声明的注解
*/</span>
<span style="color:#999999">@Test</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">void</span> <span style="color:#8be9fd">test7</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">{</span>
Class clazz <span style="color:#6272a4">=</span> Person<span style="color:#999999">.</span><span style="color:#ff79c6">class</span><span style="color:#999999">;</span>
Annotation<span style="color:#999999">[</span><span style="color:#999999">]</span> annotations <span style="color:#6272a4">=</span> clazz<span style="color:#999999">.</span><span style="color:#8be9fd">getAnnotations</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#ff79c6">for</span><span style="color:#999999">(</span>Annotation annos <span style="color:#6272a4">:</span> annotations<span style="color:#999999">)</span><span style="color:#999999">{</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>annos<span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#999999">}</span>
<span style="color:#999999">}</span>
</code></span></span></span>六、调用运行时类的指定结构
关于setAccessible方法的使用
?
Method和Field、Constructor对象都有setAccessible()方法。
?
setAccessible启动和禁用访问安全检查的开关。
? 参数值为
true则指示反射的对象在使用时应该取消Java语言访问检查。
? 提高反射的效率。如果代码中必须用反射，而该句代码需要频繁的被 调用，那么请设置为
true，使得原本无法访问的私有成员也可以访问，参数值为false则指示反射的对象应该实施Java语言访问检查。
1. 调用运行时类中指定的属性
在反射机制中，可以直接通过
Field类操作类中的属性，通过Field类提供的set()和get()方法就可以完成设置和取得属性内容的操作。
| 方法 | 作用 |
|---|---|
public Field getField(String name) | 返回此Class对象表示的类或接口的指定的public的Field |
public Field getDeclaredField(String name) | 返回此Class对象表示的类或接口的指定的Field |
在Field中：
| 方法 | 作用 |
|---|---|
public Object get(Object obj) | 取得指定对象obj上此Field的属性内容 |
public void set(Object obj,Object value) | 设置指定对象obj上此Field的属性内容 |
代码演示：
<span style="color:#000000"><span style="background-color:#282a36"><span style="color:pink"><code class="language-java"><span style="color:#ff79c6">public</span> <span style="color:#ff79c6">class</span> ReflectionTest <span style="color:#999999">{</span>
<span style="color:#999999">@Test</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">void</span> <span style="color:#8be9fd">testField</span><span style="color:#999999">(</span><span style="color:#999999">)</span> <span style="color:#ff79c6">throws</span> Exception <span style="color:#999999">{</span>
Class clazz <span style="color:#6272a4">=</span> Person<span style="color:#999999">.</span><span style="color:#ff79c6">class</span><span style="color:#999999">;</span>
<span style="color:#6272a4">//创建运行时类的对象</span>
Person p <span style="color:#6272a4">=</span> <span style="color:#999999">(</span>Person<span style="color:#999999">)</span> clazz<span style="color:#999999">.</span><span style="color:#8be9fd">newInstance</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#6272a4">//获取指定的属性：要求运行时类中属性声明为public</span>
<span style="color:#6272a4">//通常不采用此方法</span>
Field id <span style="color:#6272a4">=</span> clazz<span style="color:#999999">.</span><span style="color:#8be9fd">getField</span><span style="color:#999999">(</span><span style="color:#f1fa8c">"id"</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#6272a4">/*
设置当前属性的值
set():参数1：指明设置哪个对象的属性 参数2：将此属性值设置为多少
*/</span>
id<span style="color:#999999">.</span><span style="color:#8be9fd">set</span><span style="color:#999999">(</span>p<span style="color:#999999">,</span><span style="color:#f1fa8c">1001</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#6272a4">/*
获取当前属性的值
get():参数1：获取哪个对象的当前属性值
*/</span>
<span style="color:#ff79c6">int</span> pId <span style="color:#6272a4">=</span> <span style="color:#999999">(</span><span style="color:#ff79c6">int</span><span style="color:#999999">)</span> id<span style="color:#999999">.</span><span style="color:#8be9fd">get</span><span style="color:#999999">(</span>p<span style="color:#999999">)</span><span style="color:#999999">;</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>pId<span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#6272a4">/*
如何操作运行时类中的指定的属性 -- 需要掌握
*/</span>
<span style="color:#999999">@Test</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">void</span> <span style="color:#8be9fd">testField1</span><span style="color:#999999">(</span><span style="color:#999999">)</span> <span style="color:#ff79c6">throws</span> Exception <span style="color:#999999">{</span>
Class clazz <span style="color:#6272a4">=</span> Person<span style="color:#999999">.</span><span style="color:#ff79c6">class</span><span style="color:#999999">;</span>
<span style="color:#6272a4">//创建运行时类的对象</span>
Person p <span style="color:#6272a4">=</span> <span style="color:#999999">(</span>Person<span style="color:#999999">)</span> clazz<span style="color:#999999">.</span><span style="color:#8be9fd">newInstance</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#6272a4">//1. getDeclaredField(String fieldName):获取运行时类中指定变量名的属性</span>
Field name <span style="color:#6272a4">=</span> clazz<span style="color:#999999">.</span><span style="color:#8be9fd">getDeclaredField</span><span style="color:#999999">(</span><span style="color:#f1fa8c">"name"</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#6272a4">//2.保证当前属性是可访问的</span>
name<span style="color:#999999">.</span><span style="color:#8be9fd">setAccessible</span><span style="color:#999999">(</span><span style="color:#8be9fd">true</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#6272a4">//3.获取、设置指定对象的此属性值</span>
name<span style="color:#999999">.</span><span style="color:#8be9fd">set</span><span style="color:#999999">(</span>p<span style="color:#999999">,</span><span style="color:#f1fa8c">"Tom"</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>name<span style="color:#999999">.</span><span style="color:#8be9fd">get</span><span style="color:#999999">(</span>p<span style="color:#999999">)</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
</code></span></span></span>2. 调用运行时类中的指定的方法
通过反射，调用类中的方法，通过
Method类完成。步骤：
- 通过
Class类的getMethod(String name,Class…parameterTypes)方法取得 一个Method对象，并设置此方法操作时所需要的参数类型。- 之后使用
Object invoke(Object obj, Object[] args)进行调用，并向方法中 传递要设置的obj对象的参数信息。
Object invoke(Object obj, Object … args)
说明：
?Object对应原方法的返回值，若原方法无返回值，此时返回null? 若原方法若为静态方法，此时形参
Object obj可为null? 若原方法形参列表为空，则
Object[] args为null
? 若原方法声明为private,则需要在调用此invoke()方法前，显式调用 方法对象的setAccessible(true)方法，将可访问private的方法。
代码演示：
<span style="color:#000000"><span style="background-color:#282a36"><span style="color:pink"><code class="language-java"> <span style="color:#6272a4">/*
如何操作运行时类中的指定的方法 -- 需要掌握
*/</span>
<span style="color:#999999">@Test</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">void</span> <span style="color:#8be9fd">testMethod</span><span style="color:#999999">(</span><span style="color:#999999">)</span> <span style="color:#ff79c6">throws</span> Exception <span style="color:#999999">{</span>
Class clazz <span style="color:#6272a4">=</span> Person<span style="color:#999999">.</span><span style="color:#ff79c6">class</span><span style="color:#999999">;</span>
<span style="color:#6272a4">//创建运行时类的对象</span>
Person p <span style="color:#6272a4">=</span> <span style="color:#999999">(</span>Person<span style="color:#999999">)</span> clazz<span style="color:#999999">.</span><span style="color:#8be9fd">newInstance</span><span style="color:#999999">(</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#6272a4">/*
1.获取指定的某个方法
getDeclaredMethod():参数1 ：指明获取的方法的名称 参数2：指明获取的方法的形参列表
*/</span>
Method show <span style="color:#6272a4">=</span> clazz<span style="color:#999999">.</span><span style="color:#8be9fd">getDeclaredMethod</span><span style="color:#999999">(</span><span style="color:#f1fa8c">"show"</span><span style="color:#999999">,</span> String<span style="color:#999999">.</span><span style="color:#ff79c6">class</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#6272a4">//2.保证当前方法是可访问的</span>
show<span style="color:#999999">.</span><span style="color:#8be9fd">setAccessible</span><span style="color:#999999">(</span><span style="color:#8be9fd">true</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#6272a4">/*
3. 调用方法的invoke():参数1：方法的调用者 参数2：给方法形参赋值的实参
invoke()的返回值即为对应类中调用的方法的返回值。
*/</span>
Object returnValue <span style="color:#6272a4">=</span> show<span style="color:#999999">.</span><span style="color:#8be9fd">invoke</span><span style="color:#999999">(</span>p<span style="color:#999999">,</span><span style="color:#f1fa8c">"CHN"</span><span style="color:#999999">)</span><span style="color:#999999">;</span> <span style="color:#6272a4">//String nation = p.show("CHN");</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>returnValue<span style="color:#999999">)</span><span style="color:#999999">;</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span><span style="color:#f1fa8c">"*************如何调用静态方法*****************"</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#6272a4">// private static void showDesc()</span>
Method showDesc <span style="color:#6272a4">=</span> clazz<span style="color:#999999">.</span><span style="color:#8be9fd">getDeclaredMethod</span><span style="color:#999999">(</span><span style="color:#f1fa8c">"showDesc"</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
showDesc<span style="color:#999999">.</span><span style="color:#8be9fd">setAccessible</span><span style="color:#999999">(</span><span style="color:#8be9fd">true</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#6272a4">//如果调用的运行时类中的方法没有返回值，则此invoke()返回null</span>
<span style="color:#6272a4">// Object returnVal = showDesc.invoke(null);</span>
Object returnVal <span style="color:#6272a4">=</span> showDesc<span style="color:#999999">.</span><span style="color:#8be9fd">invoke</span><span style="color:#999999">(</span>Person<span style="color:#999999">.</span><span style="color:#ff79c6">class</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>returnVal<span style="color:#999999">)</span><span style="color:#999999">;</span><span style="color:#6272a4">//null</span>
<span style="color:#999999">}</span>
</code></span></span></span>3. 调用运行时类中的指定的构造器
代码演示：
<span style="color:#000000"><span style="background-color:#282a36"><span style="color:pink"><code class="language-java"> <span style="color:#6272a4">/*
如何调用运行时类中的指定的构造器
*/</span>
<span style="color:#999999">@Test</span>
<span style="color:#ff79c6">public</span> <span style="color:#ff79c6">void</span> <span style="color:#8be9fd">testConstructor</span><span style="color:#999999">(</span><span style="color:#999999">)</span> <span style="color:#ff79c6">throws</span> Exception <span style="color:#999999">{</span>
Class clazz <span style="color:#6272a4">=</span> Person<span style="color:#999999">.</span><span style="color:#ff79c6">class</span><span style="color:#999999">;</span>
<span style="color:#6272a4">//private Person(String name)</span>
<span style="color:#6272a4">/*
1.获取指定的构造器
getDeclaredConstructor():参数：指明构造器的参数列表
*/</span>
Constructor constructor <span style="color:#6272a4">=</span> clazz<span style="color:#999999">.</span><span style="color:#8be9fd">getDeclaredConstructor</span><span style="color:#999999">(</span>String<span style="color:#999999">.</span><span style="color:#ff79c6">class</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#6272a4">//2.保证此构造器是可访问的</span>
constructor<span style="color:#999999">.</span><span style="color:#8be9fd">setAccessible</span><span style="color:#999999">(</span><span style="color:#8be9fd">true</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#6272a4">//3.调用此构造器创建运行时类的对象</span>
Person per <span style="color:#6272a4">=</span> <span style="color:#999999">(</span>Person<span style="color:#999999">)</span> constructor<span style="color:#999999">.</span><span style="color:#8be9fd">newInstance</span><span style="color:#999999">(</span><span style="color:#f1fa8c">"Tom"</span><span style="color:#999999">)</span><span style="color:#999999">;</span>
System<span style="color:#999999">.</span>out<span style="color:#999999">.</span><span style="color:#8be9fd">println</span><span style="color:#999999">(</span>per<span style="color:#999999">)</span><span style="color:#999999">;</span>
<span style="color:#999999">}</span>
<span style="color:#999999">}</span>
</code></span></span></span>
