java 的浅拷贝 java对象浅拷贝

转载

mob64ca13f48509 2023-10-03 20:52:50

文章标签 java 的浅拷贝引用变量深拷贝浅拷贝 文章分类 Java 后端开发

什么是对象拷贝

对象拷贝即将源对象复制出一个新的对象，分配新的内存。

本文描述对象拷贝分类

分为浅拷贝和深拷贝

浅拷贝

顾名思义，简单浅层拷贝，将对象所有变量的值复制一份到新对象中。在Java中有基本数据类型和引用类型（值存放的是内存地址），而浅拷贝在处理引用对象和基本数据类型一样复制值到新对象，导致新对象的引用变量值是源对象引用变量的内存地址，也就是新对象和就对象操作引用变量是同一个。潜在相互影响隐患。

实现说明

该拷贝必须实现Cloneable接口，复写Object的clone方法
若不实现Cloneable接口会报ava.lang.CloneNotSupportedException:异常，应该是一种标准，目前暂未找到合理解释

代码实现

// 引用lombok，少写get/set,toString
import lombok.Data;

@Data
public class ShallowCopyTest implements Cloneable {

    private String name;
    private Integer age;

    private ReferenceObj referenceObj;


    @Override
    protected Object clone() {
        try {
            return super.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
            throw new RuntimeException(e.getMessage());
        }

    }

    public static void main(String[] args) {
        ShallowCopyTest shallowCopy1 = new ShallowCopyTest();
        shallowCopy1.setAge(1);
        shallowCopy1.setName("NaiNiu");
        ReferenceObj referenceObj = new ReferenceObj();
        referenceObj.setDesc("奶牛");
        referenceObj.setStatus(1);
        shallowCopy1.setReferenceObj(referenceObj);
        //shallowCopy1：[ShallowCopyTest(name=NaiNiu, age=1, referenceObj=ShallowCopyTest.ReferenceObj(desc=奶牛, status=1))]
        System.out.println("shallowCopy1：[" + shallowCopy1.toString() + "]");
        ShallowCopyTest shallowCopy2 = (ShallowCopyTest) shallowCopy1.clone();
        shallowCopy2.setName("LiMao");
        shallowCopy2.setAge(2);
        ReferenceObj referenceObj2 = shallowCopy2.getReferenceObj();
        //修改引用变量内容
        referenceObj2.setDesc("狸猫");
        referenceObj2.setStatus(2);

        //shallowCopy1：[ShallowCopyTest(name=NaiNiu, age=1, referenceObj=ShallowCopyTest.ReferenceObj(desc=狸猫, status=2))]
        //shallowCopy2：[ShallowCopyTest(name=LiMao, age=2, referenceObj=ShallowCopyTest.ReferenceObj(desc=狸猫, status=2))]
        System.out.println("shallowCopy1：[" + shallowCopy1.toString() + "]");
        System.out.println("shallowCopy2：[" + shallowCopy2.toString() + "]");
    }

    @Data
    public static class ReferenceObj implements Cloneable {
        private String desc;
        private Integer status;

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

深拷贝

顾名思义，简单浅层拷贝更深层次拷贝，即将对象所有变量的值复制一份到新对象中，并对引用变量进行深拷贝，依次深拷贝直到拷贝完成。

实现说明

该拷贝也必须实现Cloneable接口和复写Object的clone方法，引用对象变量也要实现Cloneable接口和复写Object的clone方法才能完成深拷贝，遇到引用变量需要循环拷贝直到拷贝完成。
若不实现Cloneable接口也会报ava.lang.CloneNotSupportedException:异常

代码实现

// 引用lombok，少写get/set,toString
import lombok.Data;

@Data
public class DeepCopyTest implements Cloneable {

    private String name;
    private Integer age;

    private ReferenceObj referenceObj;

    @Override
    protected Object clone() {
        try {
        	//源对象拷贝
            DeepCopyTest clone = (DeepCopyTest) super.clone();
            //将引用变量进行拷贝，若内部还有引用变量需要循环拷贝直到没有，才算完成
            ReferenceObj referenceObj = (ReferenceObj) this.getReferenceObj().clone();
            // 赋值给新对象
            clone.setReferenceObj(referenceObj);
            return clone;
        } catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException(e.getMessage());
        }


    }

    public static void main(String[] args) {
        DeepCopyTest deepCopy1 = new DeepCopyTest();
        deepCopy1.setAge(1);
        deepCopy1.setName("NaiNiu");
        ReferenceObj referenceObj = new ReferenceObj();
        referenceObj.setDesc("奶牛");
        referenceObj.setStatus(1);
        deepCopy1.setReferenceObj(referenceObj);
        //deepCopy1：[DeepCopyTest(name=NaiNiu, age=1, referenceObj=DeepCopyTest.ReferenceObj(desc=奶牛, status=1))]
        System.out.println("deepCopy1：[" + deepCopy1.toString() + "]");
        DeepCopyTest deepCopy2 = (DeepCopyTest) deepCopy1.clone();
        deepCopy2.setName("LiMao");
        deepCopy2.setAge(2);
        ReferenceObj referenceObj2 = deepCopy2.getReferenceObj();
        //修改引用变量内容
        referenceObj2.setDesc("狸猫");
        referenceObj2.setStatus(2);

        //deepCopy1：[DeepCopyTest(name=NaiNiu, age=1, referenceObj=DeepCopyTest.ReferenceObj(desc=奶牛, status=1))]
        //deepCopy2：[DeepCopyTest(name=LiMao, age=2, referenceObj=DeepCopyTest.ReferenceObj(desc=狸猫, status=2))]
        System.out.println("deepCopy1：[" + deepCopy1.toString() + "]");
        System.out.println("deepCopy2：[" + deepCopy2.toString() + "]");

    }

    @Data
    public static class ReferenceObj implements Cloneable {
        private String desc;
        private Integer status;

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