Java:Clonable 接口和拷贝

news2024/9/22 3:46:07

一 Clonable 接口

在 Java SE 中，Cloneable 是一个标记接口（Marker Interface），它位于 java.lang 包中。这个接口的主要目的是标识实现该接口的类能够被合法地克隆（即可以调用 Object 类中的 clone() 方法）。

1.当我们点入Clonable 接口的源代码中，可以发现里面什么都没有。

因为Cloneable 是一个标记接口，用来表明类的对象可以被克隆。

2.如果不实现 `Cloneable` 接口而直接调用 `clone()` 方法，系统将抛`CloneNotSupportedException` 异常。

3.Clonable 接口的实现

第一步

class Money{
    public double money=9.9;
}
public class Person {
    public String name;
    public int age;
    public Money m=new Money();

    public Person(String name,int age){
        this.name=name;
        this.age=age;
    }
    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", m=" + m +
                '}';
    }
}
public class Test {
    public static void main(String[] args) {
        Person person1=new Person("wang",10);
        Person person2=person1.
    }

}

问题：但是我们发现，在person1的引用中没有发现clone()

第二步

实现Cloneable接口，并重写Object接口的克隆方法

class Money{
     public double money=9.9;

}
public class Person implements Comparable{
    public String name;
    public int age;
    public Money m=new Money();

    public Person(String name,int age){
        this.name=name;
        this.age=age;
    }
    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", m=" + m +
                '}';
    }

    @Override
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}
public class Test {
    public static void main(String[] args) {
        Person person1=new Person("wang",10);
        Person person2=person1.clone();
    }

}

问题：但我们发现，代码依旧报错。

第三步

由于clone()方法返回值是Object是父类，所以要将克隆方法强转为子类。

class Money{
    public double money=9.9;
}
public class Person implements Comparable{
    public String name;
    public int age;
    public Money m=new Money();

    public Person(String name,int age){
        this.name=name;
        this.age=age;
    }
    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", m=" + m +
                '}';
    }

    @Override
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}
public class Test {
    public static void main(String[] args) {
        Person person1=new Person("wang",10);
        Person person2=(Person) person1.clone();
    }

}

问题：但是代码依旧报错

第四步

因为有异常，所以得先处理

class Money{
    public double money=9.9;
}
public class Person implements Comparable{
    public String name;
    public int age;
    public Money m=new Money();

    public Person(String name,int age){
        this.name=name;
        this.age=age;
    }
    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", m=" + m +
                '}';
    }

    @Override
    protected Object clone()
            throws CloneNotSupportedException {
        return super.clone();
    }
}
public class Test {
    public static void main(String[] args) 
            throws CloneNotSupportedException{
        Person person1=new Person("wang",10);
        Person person2=(Person) person1.clone();
    }

}

最终运行成功

过程如下

二拷贝

1.浅拷贝

class Money{
    public double money=9.9;
}
public class Person implements Cloneable{
    public String name;
    public int age;
    public Money m=new Money();

    public Person(String name,int age){
        this.name=name;
        this.age=age;
    }
    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", m=" + m +
                '}';
    }

    @Override
    protected Object clone()
            throws CloneNotSupportedException {
        return super.clone();
    }
}
public class Test {
    public static void main(String[] args)
            throws CloneNotSupportedException{
        Person person1=new Person("wang",10);
        Person person2=(Person) person1.clone();
/*        System.out.println(person1);
        System.out.println(person2);*/
        System.out.println("修改前"+person1.m.money);
        System.out.println("修改前"+person2.m.money);
        person1.m.money=100;
        System.out.println("修改后"+person1.m.money);
        System.out.println("修改后"+person2.m.money);
    }

}

我们可以看出，只克隆了Person对象，没有克隆Money对象，这种现象就叫做浅拷贝。

2.深拷贝

如何让Money也进行克隆呢？

接下来就是深拷贝过程

class Money implements Cloneable{
    public double money=9.9;

    @Override
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}
public class Person implements Cloneable{
    public String name;
    public int age;
    public Money m=new Money();

    public Person(String name,int age){
        this.name=name;
        this.age=age;
    }
    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", m=" + m +
                '}';
    }

    @Override
    protected Object clone()
            throws CloneNotSupportedException {
        //return super.clone();
        Person tem=(Person) super.clone();
        tem.m=(Money) this.m.clone();
        return tem;
    }
}
public class Test {
    public static void main(String[] args)
            throws CloneNotSupportedException{
        Person person1=new Person("wang",10);
        Person person2=(Person) person1.clone();
/*        System.out.println(person1);
        System.out.println(person2);*/
        System.out.println("修改前"+person1.m.money);
        System.out.println("修改前"+person2.m.money);
        person2.m.money=100;
        System.out.println("修改后"+person1.m.money);
        System.out.println("修改后"+person2.m.money);
    }

}