克隆方法clone()的使用

protected Object clone() throws CloneNotSupportedException

创建并返回此对象的副本。 “复制”的精确含义可能取决于对象的类。
对于任何对象x 表达式： x.clone() != x。只是将类“复制过来”，并不需要重新new ，这在需要很多对象的时候提供了效率上的提高

clone()方法位于java.lang.object，是protected的，使用的时候不能直接调用，需要重写。

重写的步骤是：

1、声明实现Cloneable接口。（贴标签技术，其实质并没有任何方法需要实现，类似于序列化）

2、调用super.clone拿到一个对象，如果父类的clone实现没有问题的话，在该对象的内存存储中，所有父类定义的field都已经clone好了，该类中的primitive（基本数据类型）和不可变类型（string）引用也克隆好了，可变类型引用都是浅copy。

3、把浅copy的引用指向原型对象新的克隆体。

写两个例子

第一个是浅克隆

/**
* @author 逸川同学
* 浅克隆
* 只要数据都是基本数据类型或者String类型，可以克隆一次
*/
public class Client {
public static void main(String[] args) {
Person person = new Person("jack",22);
Person person2 = null;
try {
person2 = (Person) person.clone();
person2.setName("Rose");
person2.setAge(19);
} catch (CloneNotSupportedException e) {
e.printStackTrace();
}
System.out.println(person);
System.out.println(person2);
}
}

public class Person implements Cloneable{
private String name;
private int age;
public Person() {
}
public Person(String name, int age) {
super();
this.name = name;
this.age = age;
}
/**
* @return the name
*/
public String getName() {
return name;
}
/* (non-Javadoc)
* @see java.lang.Object#toString()
*/
@Override
public String toString() {
return "Person [name=" + name + ", age=" + age + "]";
}
/**
* @param name the name to set
*/
public void setName(String name) {
this.name = name;
}
/**
* @return the age
*/
public int getAge() {
return age;
}
/**
* @param age the age to set
*/
public void setAge(int age) {
this.age = age;
}
@Override
protected Object clone() throws CloneNotSupportedException {
return super.clone();
}
}


第二个是深克隆
/**
* @author 逸川同学
* 深克隆
* 非基本数据类型需要进行深克隆
*/
public class Client {
public static void main(String[] args) {
Acount acount1 = new Acount(new Person("Jack",21),100);
Acount acount2 = null;
try {
acount2 = (Acount)acount1.clone();
acount2.setPerson(new Person("Rose",20));
acount2.setBalance(200);
} catch (CloneNotSupportedException e) {
e.printStackTrace();
}
System.out.println(acount1);
System.out.println(acount2);
}
}
public class Acount implements Cloneable{
private Person person;
private double balance;
public Acount(Person person, double balance) {
super();
this.person = person;
this.balance = balance;
}
public Acount() {
}
@Override
public String toString() {
return "Acount [person=" + person + ", balance=" + balance + "]";
}
public Person getPerson() {
return person;
}
public void setPerson(Person person) {
this.person = person;
}
public double getBalance() {
return balance;
}
public void setBalance(double balance) {
this.balance = balance;
}
//克隆，进行深克隆
@Override
public Object clone() throws CloneNotSupportedException {
Acount acount = (Acount) super.clone();
if(person != null){//防范空指针异常
acount.person = (Person) acount.person.clone();
}
return acount;
}
}

public class Person implements Cloneable{
private String name;
private int age;
public Person() {
}
public Person(String name, int age) {
super();
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
@Override
public String toString() {
return "Person [name=" + name + ", age=" + age + "]";
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public Object clone() throws CloneNotSupportedException {
return super.clone();
}
}