1.static 修饰符应用范围

static修饰符只能用来修饰类中定义的成员变量、成员方法、代码块以及内部类(内部类有专门章节进行讲解)。

2.static 修饰成员变量

static 修饰的成员变量称之为类变量。属于该类所有成员共享。

示例

package cn.lyxq.test04;

public class ChinesePeople {

    private String name;

    private  int age;

    public static String country = "中国";

    public ChinesePeople(String name,int age){
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

package cn.lyxq.test04;

public class ChinesePeopleTest {

    public static void main(String[] args) {
        ChinesePeople cp1 = new ChinesePeople("张三",20);
        System.out.println(ChinesePeople.country);
        ChinesePeople.country="日本";

        ChinesePeople cp2 = new ChinesePeople("李四",30);
        System.out.println(ChinesePeople.country);

        ChinesePeople cp3 = new ChinesePeople("王五",32);
        System.out.println(ChinesePeople.country);
    }


}

如果类变量是公开的，那么可以使用 类名.变量名 直接访问该类变量

3.static 修饰成员方法

static 修饰的成员方法称之为类方法，属于该类所有成员共享。

package cn.lyxq.test04;

public class ChinesePeople {

    private String name;

    private  int age;

    private static String country = "中国";

    public ChinesePeople(String name,int age){
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
    //类方法
    public static String getCountry() {
        return country;
    }
    //类方法
    public static void setCountry(String country) {
        ChinesePeople.country = country;
    }
}

package cn.lyxq.test04;

public class ChinesePeopleTest {

    public static void main(String[] args) {
        ChinesePeople cp1 = new ChinesePeople("张三",20);

        ChinesePeople.setCountry("日本");

        ChinesePeople cp2 = new ChinesePeople("李四",30);
        System.out.println(ChinesePeople.getCountry());

        ChinesePeople cp3 = new ChinesePeople("王五",32);
        System.out.println(cp3.getCountry());//不是最优访问方式
    }


}

如果类方法是公开的，那么可以使用 类名.方法名直接访问该类方法。

4.static 修饰代码块

static 修饰的代码块被称为静态代码块，在JVM第一次记载该类时执行。因此，静态代码代码块只能执行一次，通常用于一些系统设置场景。

package cn.lyxq.test04;

public class ChinesePeople {

    private String name;

    private  int age;
    //使用static修饰的成员变量称为类变量，不会随着成员变化而变化，属于所有成员共享
    private static String country ;
    //static修饰的代码块称为静态代码块，在JVM第一次加载该类的时候执行，只能执行一次
    static{
        country = "中国";
        System.out.println("country属性已经被赋值");
    }

    public ChinesePeople(String name,int age){
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
    //类方法
    public static String getCountry() {
        return country;
    }
    //类方法
    public static void setCountry(String country) {
        ChinesePeople.country = country;
    }
}

package cn.lyxq.test04.test;

import  cn.lyxq.test04.ChinesePeople;

public class ChinesePeopleTest {

    public static void main(String[] args) {
        ChinesePeople cp = new ChinesePeople("张三",20);
    }


}

5.static内存