Java中Cloneable 和 clone()的总结和使用
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。