Java 深copy 浅copy 引用copy

大家好，我是烤鸭：

今天分享一下浅copy和深copy。

1. 深copy

什么是深copy，只复制原对象属性值，不管地址。

说一下业务场景：

如果我想创建一个对象，只是对原对象的某个属性值改变。普通的做法就是new 一个对象，然后setXXX，如果属性特别多的话不方便，这时候就是需要深copy。复制出来的对象属于不同的地址，改变复制对象的属性值不会影响原对象。

TestClone.java：

package com.xxx.xxx.utils;import org.junit.Test;import java.io.Serializable;/*** Created by  on 2018/7/23*/
public class TestClone {public TestClone() {}@Testpublic void testDeepCopy(){Person person1 = new Person();person1.id = "id1";person1.name = "name1";person1.sex = "sex1";System.out.println("复制前person:"+person1);Person clone = CloneUtils.clone(person1);System.out.println("这是深copy后的对象:"+clone);System.out.println("=========改变深copy后的对象属性=====================");clone.id = "id2";clone.name = "name2";clone.sex = "sex2";System.out.println("copy的对象:"+clone);System.out.println("复制后person:"+person1);}}
class Person implements Serializable,Cloneable{String id;String name;String sex;public String getId() {return id;}public void setId(String id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getSex() {return sex;}public void setSex(String sex) {this.sex = sex;}@Overridepublic String toString() {return "Person{" +"id='" + id + '\'' +", name='" + name + '\'' +", sex='" + sex + '\'' +'}';}@Overridepublic Person clone() {Person person = null;try {person = (Person) super.clone();} catch (CloneNotSupportedException ignored) {System.out.println(ignored.getMessage());}return person;}
}

CloneUtils.java：

package com.xxx.xxx.utils;import java.io.*;public class CloneUtils {@SuppressWarnings("unchecked")public static <T extends Serializable> T clone(T obj){T cloneObj = null;try {//写入字节流ByteArrayOutputStream out = new ByteArrayOutputStream();ObjectOutputStream obs = new ObjectOutputStream(out);obs.writeObject(obj);obs.close();//分配内存，写入原始对象，生成新对象ByteArrayInputStream ios = new ByteArrayInputStream(out.toByteArray());ObjectInputStream ois = new ObjectInputStream(ios);//返回生成的新对象cloneObj = (T) ois.readObject();ois.close();} catch (Exception e) {e.printStackTrace();}return cloneObj;}
}

结果如图：

2. 浅copy

与深copy相对应，浅copy就是复制的对象指向了原对象的地址值。如果复制的对象属性值改变，原对象也会随之改变。

如果是单个对象的话，用引用copy吧。

如果是对象中还有属性是对象的话。

Person.java 和 Man.java

class Person  implements Cloneable, Serializable  {String id;String name;String sex;Man man;public String getId() {return id;}public void setId(String id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getSex() {return sex;}public void setSex(String sex) {this.sex = sex;}public Man getMan() {return man;}public void setMan(Man man) {this.man = man;}@Overridepublic String toString() {return "Person{" +"id='" + id + '\'' +", name='" + name + '\'' +", sex='" + sex + '\'' +", man=" + man +'}';}@Overridepublic Person clone() {Person person = null;try {person = (Person) super.clone();} catch (CloneNotSupportedException ignored) {System.out.println(ignored.getMessage());}return person;}
}
class Man{String name;String age;public String getName() {return name;}public void setName(String name) {this.name = name;}public String getAge() {return age;}public void setAge(String age) {this.age = age;}@Overridepublic String toString() {return "Man{" +"name='" + name + '\'' +", age='" + age + '\'' +'}';}
}

 /*** 浅复制* @throws IOException* @throws ClassNotFoundException*/@Testpublic void testShallowCopy() throws IOException, ClassNotFoundException {Person person1 = new Person();Man man = new Man();man.name = "man1";man.age = "age1";person1.id = "id1";person1.name = "name1";person1.sex = "sex1";person1.man = man;System.out.println("复制前person:"+person1);Person clone = person1.clone();System.out.println("这是浅copy后的对象:"+clone);System.out.println("=========改变浅copy后的对象属性=====================");clone.id = "id2";clone.name = "name2";clone.sex = "sex2";clone.man.name = "man2";clone.man.age = "age2";System.out.println("copy的对象:"+clone);System.out.println("复制后person:"+person1);}

如图：

可以看出，改变了man的属性，原对象中的man属性值也改变了。这就是浅copy。

如果不想这样的话，就把man也clone。

man实现clone接口，重写clone方法：

class Man implements Cloneable{String name;String age;public String getName() {return name;}public void setName(String name) {this.name = name;}public String getAge() {return age;}public void setAge(String age) {this.age = age;}@Overridepublic String toString() {return "Man{" +"name='" + name + '\'' +", age='" + age + '\'' +'}';}@Overrideprotected Object clone() throws CloneNotSupportedException {return super.clone();}
}

修改copy方法：

        Man man2 = (Man) person1.man.clone();man2.name = "man2";man2.age = "age2";clone.man = man2;

如图：

3. 引用copy

  /*** 引用复制* @throws IOException* @throws ClassNotFoundException*/@Testpublic void testQuoteCopy() throws IOException, ClassNotFoundException {Person person1 = new Person();person1.id = "id1";person1.name = "name1";person1.sex = "sex1";System.out.println("复制前person:"+person1);Person clone = person1;System.out.println("这是引用copy后的对象:"+clone);System.out.println("=========改变引用copy后的对象属性=====================");clone.id = "id2";clone.name = "name2";clone.sex = "sex2";System.out.println("copy的对象:"+clone);System.out.println("复制后person:"+person1);}

如图：