无论是在java面试过程中，还是在与各种老鸟交流的过程中，对java对象的深浅拷贝，都是一个绕不开的问题，这个问题看似很容易，却是大多数人用来区分小白的标准问题。现在对该问题进行说明。
1.定义
浅克隆（拷贝）：复制一个对象的实例，但是这个对象中包含的其它的对象还是共用的。一般用super.clone()方法，clone的对象就是浅克隆。
深克隆（拷贝）：复制一个对象的实例，而且这个对象中包含的其它的对象也要复制一份。如果使用clone()，那么需要对clone方法进行重写，复制一个对象super.clone()，之后再一一对属性进行复制。这样显得非常冗余，幸好，在java中还可以通过流来实现。但是注意，对象需要实现Serializable接口。
2.举例
有如下类Husband, Husband又引用了Wife。
类结构图
Wife类
package com.dhb.CloneTest;
import lombok.Data;
import java.io.Serializable;
import java.util.Date;
@Data
public class Wife implements Serializable {
private String name;
private Date birthday;
public Wife() {
this.name = "思思";
this.birthday = new Date();
}
public Wife(String name, Date birthday) {
this.name = name;
this.birthday = birthday;
}
}
Husband类
package com.dhb.CloneTest;
import lombok.Data;
import java.io.*;
import java.util.Date;
@Data
public class Husband implements Cloneable,Serializable {
private Wife wife;
private Date birthday;
public Husband() {
this.wife = new Wife();
this.birthday = new Date();
}
public Husband(Wife wife, Date birthday) {
this.wife = wife;
this.birthday = birthday;
}
public Object clone() {
Husband husband = null;
try {
husband = (Husband) super.clone();
} catch (CloneNotSupportedException e) {
e.printStackTrace();
}finally {
return husband;
}
}
public Object deepClone() throws IOException, ClassNotFoundException {
ByteArrayOutputStream bos = new ByteArrayOutputStream();
ObjectOutputStream oos = new ObjectOutputStream(bos);
oos.writeObject(this);
ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());
ObjectInputStream ois = new ObjectInputStream(bis);
return ois.readObject();
}
}
在Husband类中存在clone和deepClone方法。现在对这两个方法进行测试。
package com.dhb.CloneTest;
import java.io.IOException;
public class CloneTest {
public static void main(String[] args) {
try {
Husband husband = new Husband();
System.out.println("husband birthday is :"+husband.getBirthday());
System.out.println("wife birthday is :"+husband.getWife().getBirthday());
System.out.println("***********************************************");
Husband husband1 = (Husband) husband.clone();
System.out.println("husband1 birthday is :"+husband1.getBirthday());
System.out.println("wife birthday is :"+husband1.getWife().getBirthday());
System.out.println("***********************************************");
System.out.println("husband 是否相同："+(husband == husband1));
System.out.println("wife 是否相同："+(husband.getWife() == husband1.getWife()));
System.out.println("***********************************************");
Husband husband2 = (Husband) husband.deepClone();
System.out.println("husband2 birthday is :"+husband2.getBirthday());
System.out.println("wife birthday is :"+husband2.getWife().getBirthday());
System.out.println("***********************************************");
System.out.println("husband 是否相同："+(husband == husband2));
System.out.println("wife 是否相同："+(husband.getWife() == husband2.getWife()));
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
}
运行结果：
husband birthday is :Mon Aug 07 19:03:38 CST 2017
wife birthday is :Mon Aug 07 19:03:38 CST 2017
***********************************************
husband1 birthday is :Mon Aug 07 19:03:38 CST 2017
wife birthday is :Mon Aug 07 19:03:38 CST 2017
***********************************************
husband 是否相同：false
wife 是否相同：true
***********************************************
husband2 birthday is :Mon Aug 07 19:03:38 CST 2017
wife birthday is :Mon Aug 07 19:03:38 CST 2017
***********************************************
husband 是否相同：false
wife 是否相同：false
注：上述代码中的@Data 是lombak的一个注解。
当然，实现深克隆的方法并不局限于流这一种办法，还可以通过json等其他办法实现。
