浅谈Java中的克隆机制

Posted 2021-05-07 erinchen

转 https://blog.csdn.net/zhaoheng314/article/details/81985880

 

Java语言中克隆针对的是类的实例

/Library/Java/JavaVirtualMachines/jdk1.8.0_221.jdk/Contents/Home/jre/lib/rt.jar!/java/lang/Cloneable.class

根据Cloneable接口的注释, 克隆需要遵循以下规则：

1. 必须实现Cloneable接口
2. 实现Cloneable的类应该重写clone()，重写时该方法的修饰符为public。

　　

/Library/Java/JavaVirtualMachines/jdk1.8.0_221.jdk/Contents/Home/jre/lib/rt.jar!/java/lang/Object.class

protected native Object clone() throws CloneNotSupportedException;


age属性是int类型，基本类型克隆时只是传值，不存在传引用
String类 final关键字 不可变特性，克隆对象修改了name属性的引用


深克隆

public class Student implements Cloneable{

    private String name;//引用类型  final关键字 一是不可变，二是禁止指令重排

    private int age;//基本类型

    private Classes classes;//引用类型

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

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

    public void setClasses(Classes classes){
        this.classes = classes;
    }

    public String getName(){
        return name;
    }

    public Classes getClasses(){
        return classes;
    }

    @Override
    public String toString() {
        return "Student [name=" + name + ", age=" + age + ", classes=" + classes + "]";
    }

    @Override
    protected Object clone() throws CloneNotSupportedException {
        Student stu = (Student)super.clone();
        //克隆classes属性时候调用Classes类的clone();
        Classes cla = (Classes)classes.clone();
        stu.setClasses(cla);
        return stu;
    }
}

 

public class Classes implements Cloneable{

    private int classId;//基本类型

    private String className;//引用类型

    public void setClassId(int classId){
        this.classId = classId;
    }

    public void  setClassName(String className){
        this.className = className;
    }


    @Override
    public String toString() {
        return "Classes [classId=" + classId + ", className=" + className + "]";
    }

    @Override
    protected Object clone() throws CloneNotSupportedException{
        return super.clone();
    }
}

public class TestClone {
    public static void main(String[] args) {
        Student stu = new Student();
        stu.setName("张三");
        stu.setAge(10);

        Classes classes = new Classes();
        classes.setClassId(101);
        classes.setClassName("一班");
        stu.setClasses(classes);


        try{
            System.out.println("深克隆测试-----");
            //克隆
            Student stu2 = (Student)stu.clone();
            System.out.println("两个对象是否相同：" + (stu == stu2));
            System.out.println("两个对象name属性是否相同：" + (stu.getName() == stu2.getName()));
            System.out.println("两个对象classes是否相同：" + (stu.getClasses() == stu2.getClasses()));
            System.out.println("深克隆，Stu" + stu);
            System.out.println("深克隆，Stu2" + stu2);

            System.out.println("修改克隆对象属性");
            stu2.setName("李四"); // public final class String 一是不可变，二是禁止指令重排 修改了name属性的引用
            stu2.setAge(20);
            stu2.getClasses().setClassId(102);
            stu2.getClasses().setClassName("二班");
            System.out.println("修改克隆对象属性后，Stu " + stu);
            System.out.println("修改克隆对象属性后，Stu2 " + stu2);

        }catch (CloneNotSupportedException e){
            e.printStackTrace();
        }



    }
}