java中clone的用法_java clone是浅拷贝吗

全栈程序员站长

发布于 2022-11-04 15:42:04

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发布于 2022-11-04 15:42:04

一.Cloneable 的用途

Cloneable和Serializable一样都是标记型接口，它们内部都没有方法和属性，implements Cloneable表示该对象能被克隆，能使用Object.clone()方法。如果没有implements Cloneable的类调用Object.clone()方法就会抛出CloneNotSupportedException。

二.克隆的分类

(1)浅克隆（shallow clone），浅拷贝是指拷贝对象时仅仅拷贝对象本身和对象中的基本变量，而不拷贝对象包含的引用指向的对象。 (2)深克隆（deep clone），深拷贝不仅拷贝对象本身，而且拷贝对象包含的引用指向的所有对象。

举例区别一下：对象A1中包含对B1的引用，B1中包含对C1的引用。浅拷贝A1得到A2，A2中依然包含对B1的引用，B1中依然包含对C1的引用。深拷贝则是对浅拷贝的递归，深拷贝A1得到A2，A2中包含对B2（B1的copy）的引用，B2中包含对C2（C1的copy）的引用。

三.克隆的举例

要让一个对象进行克隆，其实就是两个步骤： 1. 让该类实现java.lang.Cloneable接口； 2. 重写（override）Object类的clone()方法。

public class Wife implements Cloneable { 
  
private int id;  
private String name;  
public int getId() {  
return id;  
}  
public void setId(int id) {  
this.id = id;  
}  
public String getName() {  
return name;  
}  
public void setName(String name) {  
this.name = name;  
}  
public Wife(int id,String name) {  
this.id = id;  
this.name = name;  
}  
@Override  
public int hashCode() {
//myeclipse自动生成的 
final int prime = 31;  
int result = 1;  
result = prime * result + id;  
result = prime * result + ((name == null) ? 0 : name.hashCode());  
return result;  
}  
@Override  
public boolean equals(Object obj) {
//myeclipse自动生成的 
if (this == obj)  
return true;  
if (obj == null)  
return false;  
if (getClass() != obj.getClass())  
return false;  
Wife other = (Wife) obj;  
if (id != other.id)  
return false;  
if (name == null) {  
if (other.name != null)  
return false;  
} else if (!name.equals(other.name))  
return false;  
return true;  
}  
@Override  
public Object clone() throws CloneNotSupportedException {  
return super.clone();  
}  
/** * @param args * @throws CloneNotSupportedException */  
public static void main(String[] args) throws CloneNotSupportedException {  
Wife wife = new Wife(1,"wang");  
Wife wife2 = null;  
wife2 = (Wife) wife.clone();  
System.out.println("class same="+(wife.getClass()==wife2.getClass()));//true 
System.out.println("object same="+(wife==wife2));//false 
System.out.println("object equals="+(wife.equals(wife2)));//true 
}  
}

四.浅克隆的举例

public class Husband implements Cloneable { 
  
private int id;  
private Wife wife;  
public Wife getWife() {  
return wife;  
}  
public void setWife(Wife wife) {  
this.wife = wife;  
}  
public int getId() {  
return id;  
}  
public void setId(int id) {  
this.id = id;  
}  
public Husband(int id) {  
this.id = id;  
}  
@Override  
public int hashCode() {
//myeclipse自动生成的 
final int prime = 31;  
int result = 1;  
result = prime * result + id;  
return result;  
}  
@Override  
protected Object clone() throws CloneNotSupportedException {  
return super.clone();  
}  
@Override  
public boolean equals(Object obj) {
//myeclipse自动生成的 
if (this == obj)  
return true;  
if (obj == null)  
return false;  
if (getClass() != obj.getClass())  
return false;  
Husband other = (Husband) obj;  
if (id != other.id)  
return false;  
return true;  
}  
/** * @param args * @throws CloneNotSupportedException */  
public static void main(String[] args) throws CloneNotSupportedException {  
Wife wife = new Wife(1,"jin");  
Husband husband = new Husband(1);  
Husband husband2 = null;  
husband.setWife(wife);  
husband2 = (Husband) husband.clone();  
System.out.println("husband class same="+(husband.getClass()==husband2.getClass()));//true 
System.out.println("husband object same="+(husband==husband2));//false 
System.out.println("husband object equals="+(husband.equals(husband)));//true 
System.out.println("wife class same="+(husband.getWife().getClass()==husband2.getWife().getClass()));//true 
System.out.println("wife object same="+(husband.getWife()==husband2.getWife()));//true 
System.out.println("wife object equals="+(husband.getWife().equals(husband.getWife())));//true 
}  
}

五.深克隆的举例

如果要深克隆，需要重写（override）Object类的clone()方法，并且在方法内部调用持有对象的clone()方法；注意如下代码的clone()方法

public class Husband implements Cloneable { 
  
private int id;  
private Wife wife;  
public Wife getWife() {  
return wife;  
}  
public void setWife(Wife wife) {  
this.wife = wife;  
}  
public int getId() {  
return id;  
}  
public void setId(int id) {  
this.id = id;  
}  
public Husband(int id) {  
this.id = id;  
}  
@Override  
public int hashCode() {
//myeclipse自动生成的 
final int prime = 31;  
int result = 1;  
result = prime * result + id;  
return result;  
}  
@Override  
protected Object clone() throws CloneNotSupportedException {  
Husband husband = (Husband) super.clone();  
husband.wife = (Wife) husband.getWife().clone();  
return husband;  
}  
@Override  
public boolean equals(Object obj) {
//myeclipse自动生成的 
if (this == obj)  
return true;  
if (obj == null)  
return false;  
if (getClass() != obj.getClass())  
return false;  
Husband other = (Husband) obj;  
if (id != other.id)  
return false;  
return true;  
}  
/** * @param args * @throws CloneNotSupportedException */  
public static void main(String[] args) throws CloneNotSupportedException {  
Wife wife = new Wife(1,"jin");  
Husband husband = new Husband(1);  
Husband husband2 = null;  
husband.setWife(wife);  
husband2 = (Husband) husband.clone();  
System.out.println("husband class same="+(husband.getClass()==husband2.getClass()));//true 
System.out.println("husband object same="+(husband==husband2));//false 
System.out.println("husband object equals="+(husband.equals(husband)));//true 
System.out.println("wife class same="+(husband.getWife().getClass()==husband2.getWife().getClass()));//true 
System.out.println("wife object same="+(husband.getWife()==husband2.getWife()));//false 
System.out.println("wife object equals="+(husband.getWife().equals(husband.getWife())));//true 
}  
}

但是也有不足之处，如果Husband内有N个对象属性，突然改变了类的结构，还要重新修改clone()方法。解决办法：可以使用Serializable运用反序列化手段，调用java.io.ObjectInputStream对象的 readObject()方法。

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原始发表：2022年10月14日，如有侵权请联系 cloudcommunity@tencent.com 删除

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