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object.clone()在java中是如何工作的?

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我试图了解Object类的clone()方法的工作原理 . Object类中的注释表示' this method performs a "shallow copy" of this object, not a "deep copy" operation. '

以下是我对Shallow&Deep copy的理解..

浅拷贝尽可能少复制 . 集合的浅表副本是集合结构的副本,而不是元素 . 通过浅拷贝,两个集合现在共享各个元素 . 深拷贝复制一切 . 集合的深层副本是两个集合,原始集合中的所有元素都是重复的 .

因此,如果我克隆一个Object并修改其克隆上的任何可变元素,那么同样应该反映在创建克隆的第一个对象上,因为它们共享相同的内存 . 为了测试这个,我创建了3个类......

一个简单的pojo ..

package test.clone;

import java.util.Arrays;

public class Misc implements Cloneable{
    private String value;

    public Misc(String value) {
        super();
        this.value = value;
    }

    public String getValue() {
        return value;
    }

    public void setValue(String value) {
        this.value = value;
    }

    @Override
    public String toString() {
        return "Misc [value=" + value + "]";
    }


    protected Misc clone() throws CloneNotSupportedException{
        return (Misc)super.clone();
    }

}

需要克隆的类..

package test.clone;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;


public class Victim implements Cloneable{
    private String name = "Renjith";
    private String[] educationList = {"EDU_1", "EDU_2", "EDU_3", "EDU_4"};
    private Misc[] miscList = {new Misc("1"), new Misc("2")};
    private List<Misc> miscList2 = new ArrayList<Misc>(Arrays.asList(miscList));

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String[] getEducationList() {
        return educationList;
    }
    public void setEducationList(String[] educationList) {
        this.educationList = educationList;
    }

    protected Victim clone() throws CloneNotSupportedException{
        return (Victim)super.clone();
    }
    public Misc[] getMiscList() {
        return miscList;
    }
    public void setMiscList(Misc[] miscList) {
        this.miscList = miscList;
    }


    public List<Misc> getMiscList2() {
        return miscList2;
    }
    public void setMiscList2(List<Misc> miscList2) {
        this.miscList2 = miscList2;
    }
    @Override
    public String toString() {
        return "Victim [name=" + name + ", educationList="
                + Arrays.toString(educationList) + ", miscList="
                + Arrays.toString(miscList) + ", miscList2=" + miscList2 + "]";
    }



}

进行克隆的主要类......和修改......

public class Main {

    public static void main(String[] args) throws CloneNotSupportedException {
        Victim victim = new Victim();

        System.out.println(victim);

        Victim secondVictim = victim.clone();

        String[] educationList = {"EDU_1_mod", "EDU_2_mod", "EDU_3_mod", "EDU_4_mod"};
        Misc[] miscList = {new Misc("3"), new Misc("4")};
        List<Misc> miscList2 = new ArrayList<Misc>(Arrays.asList(miscList));

        secondVictim.setEducationList(educationList);
        secondVictim.setMiscList(miscList);
        secondVictim.setMiscList2(miscList2);

        System.out.println(secondVictim);

        System.out.println(victim);
    }

}

我期待输出如下......

受害者[name = Renjith,educationList = [EDU_1,EDU_2,EDU_3,EDU_4],miscList = [Misc [value = 1],Misc [value = 2]],miscList2 = [Misc [value = 1],Misc [value] = 2]]]受害者[name = Renjith,educationList = [EDU_1_mod,EDU_2_mod,EDU_3_mod,EDU_4_mod],miscList = [Misc [value = 3],Misc [value = 4]],miscList2 = [Misc [value = 3] ,Misc [value = 4]]]受害者[name = Renjith,educationList = [EDU_1,EDU_2,EDU_3,EDU_4],miscList = [Misc [value = 3],Misc [value = 4]],miscList2 = [Misc [值= 3],杂项[value = 4]]]

但我得到......

受害者[name = Renjith,educationList = [EDU_1,EDU_2,EDU_3,EDU_4],miscList = [Misc [value = 1],Misc [value = 2]],miscList2 = [Misc [value = 1],Misc [value] = 2]]]受害者[name = Renjith,educationList = [EDU_1_mod,EDU_2_mod,EDU_3_mod,EDU_4_mod],miscList = [Misc [value = 3],Misc [value = 4]],miscList2 = [Misc [value = 3] ,Misc [value = 4]]]受害者[name = Renjith,educationList = [EDU_1,EDU_2,EDU_3,EDU_4],miscList = [Misc [value = 1],Misc [value = 2]],miscList2 = [Misc [值= 1],杂项[value = 2]]]

谁能告诉我这有什么问题?

我已经经历了Understanding Object.clone() in Java,但仍然无法理解....

1 回答

  • 2

    您没有修改列表/数组,而是用新引用替换它们 . 尝试像这样更新你的setter:

    public void setMiscList(Misc[] miscList) {
        this.miscList[0] = miscList[0];
        this.miscList[1] = miscList[1];
    }
    
    public void setMiscList2(List<Misc> miscList2) {
        this.miscList2.set(0, miscList2.get(0));
        this.miscList2.set(1, miscList2.get(1));
    }
    

    这应该修改共享对象,从而产生预期的输出 .

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