java如何实现对象的克隆

一.java实现对象的克隆有两种方式

1.继承object类重写clone方法;

假如我现在要克隆一个学生对象,该对象拥有一些属性,例如:姓名;首先创建学生类

package com.onekeyop.sop.bingfa;

public class Student {
    private String xuehao;
    private String name;
    private String zhiye;
    private String xingbie;
    private String nianling;
    private String aihao;

    public String getXuehao() {
        return xuehao;
    }

    public void setXuehao(String xuehao) {
        this.xuehao = xuehao;
    }

    public String getName() {
        return name;
    }

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

    public String getZhiye() {
        return zhiye;
    }

    public void setZhiye(String zhiye) {
        this.zhiye = zhiye;
    }

    public String getXingbie() {
        return xingbie;
    }

    public void setXingbie(String xingbie) {
        this.xingbie = xingbie;
    }

    public String getNianling() {
        return nianling;
    }

    public void setNianling(String nianling) {
        this.nianling = nianling;
    }

    public String getAihao() {
        return aihao;
    }

    public void setAihao(String aihao) {
        this.aihao = aihao;
    }
    //通过覆盖超类的clone方法来实现克隆
    @Override
    public Object clone() {
        Student stu = null;
        try{
            stu = (Student)super.clone();
        }catch(CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return stu;
    }
}
该学生类继承了所有类的超类Object;
关键地方在于对超类中的clone方法的重写;
下面我们新建一个测试类ADDThread

package com.onekeyop.sop.bingfa;


import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;

public class AddThread extends Thread{
     
    public static void main(String[] args){
        
        Map<String,String> xuesheng = new HashMap<>();
        Map<String,String> xuesheng2 = new HashMap<>();
        //首先创建一个学生对象
        Student zhangqingjiao = new Student();

        //java中只能传递对值的引用,而不能传递值
         
        zhangqingjiao.setAihao("钓鱼");
        zhangqingjiao.setName("张发菜");
        zhangqingjiao.setNianling("22");
        zhangqingjiao.setXingbie("男");
        zhangqingjiao.setZhiye("程序员");
        zhangqingjiao.setXuehao("2014551522");
        //将对象的属性放入键值对中
        xuesheng.put("爱好",zhangqingjiao.getAihao());
        xuesheng.put("姓名",zhangqingjiao.getName());
        xuesheng.put("年龄",zhangqingjiao.getNianling());
        xuesheng.put("性别",zhangqingjiao.getXingbie());
        xuesheng.put("职业",zhangqingjiao.getZhiye());
        xuesheng.put("学号",zhangqingjiao.getZhiye());
        System.out.println(xuesheng);
        try {
            Student zhangqingjiao2 = (Student) zhangqingjiao.clone();
        }catch (Exception e){
            e.printStackTrace();
        }

        //***********
        xuesheng2.put("爱好",zhangqingjiao.getAihao());
        xuesheng2.put("姓名",zhangqingjiao.getName());
        xuesheng2.put("年龄",zhangqingjiao.getNianling());
        xuesheng2.put("性别",zhangqingjiao.getXingbie());
        xuesheng2.put("职业",zhangqingjiao.getZhiye());
        xuesheng2.put("学号",zhangqingjiao.getZhiye());
        //接下来就要克隆一个对象


        System.out.println(xuesheng);
        //克隆开始
        //Student zhangqingjiao2=zhangqingjiao;
        System.out.println(xuesheng2);

        Thread thread1 = new Thread();
        Thread thread2 = new Thread();
        System.out.println("see two see");
        System.out.println(xuesheng.equals(xuesheng2));
        System.out.println(xuesheng==xuesheng2);
        System.out.println(xuesheng.hashCode());
        String s="A";
        System.out.println(s.hashCode());
    }
    
}
其中,我们运用了map工具类,来存放学生对象拥有的一些属性
输出结果如下:
{学号=程序员, 性别=男, 姓名=张发菜, 职业=程序员, 年龄=22, 爱好=钓鱼}
{学号=程序员, 性别=男, 姓名=张发菜, 职业=程序员, 年龄=22, 爱好=钓鱼}
{学号=程序员, 性别=男, 姓名=张发菜, 职业=程序员, 年龄=22, 爱好=钓鱼}

结果能输出正确,并且编译器还报了异常
java.lang.CloneNotSupportedException: com.onekeyop.sop.bingfa.Student
    at java.lang.Object.clone(Native Method)
    at com.onekeyop.sop.bingfa.Student.clone(Student.java:63)
    at com.onekeyop.sop.bingfa.AddThread.main(AddThread.java:35)
这个异常说是克隆不支持异常;
由于克隆,是对值的赋值,而不是对引用的赋值,查看jdk源码,你就会发现

protected native Object clone() throws CloneNotSupportedException;
克隆方法是通过java本地方法实现,因为此方法要和cpu底层打交道