java clone方法

package test1;

import java.util.Date;
import java.util.GregorianCalendar;

public class CloneTest {

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
try {
Employee original = new Employee("john Q. Public",5000);
original.setHireDay(2000, 1, 1);
Employee copy = original.clone();
copy.raiseSalary(10);
copy.setHireDay(2002, 12, 31);
System.out.println("original=" + original);
System.out.println("copy=" + copy);

} catch (Exception e) {
// TODO: handle exception
e.printStackTrace();
}
}

}

class Employee implements Cloneable{

private String name;
private double salary;
private Date hireDay;

public Employee(String n,double s){
name = n;
salary = s;
hireDay = new Date();
}

public Employee clone() throws CloneNotSupportedException{
Employee cloned = (Employee) super.clone();

cloned.hireDay = (Date) hireDay.clone();

return cloned;
}

public void setHireDay(int year,int month,int day){
Date newHireDay = new GregorianCalendar(year,month-1,day).getTime();

hireDay.setTime(newHireDay.getTime());
}

public void raiseSalary(double byPercent){
double raise = salary * byPercent /100;
salary += raise;
}

public String toString(){
return "Employee[name="+name+",salary="+salary+",hireDay="+hireDay+"]";
}

}

输出结果：

original=Employee[name=john Q. Public,salary=5000.0,hireDay=Sat Jan 01 00:00:00 CST 2000]

copy=Employee[name=john Q. Public,salary=5500.0,hireDay=Tue Dec 31 00:00:00 CST 2002]

学习小结：

在对各个域进行对应的拷贝时，如果对象中包含了子对象的引用，拷贝的结果会是的两个域引用同一个子对象

因此原始对象与拷贝对象共享这部分信息。若这部分信息不会发生改变时，则进行浅拷贝（默认拷贝）即可，但是

如果这部分信息会发生改变，那么需要进行深拷贝，以防止一个对象对这部分信息的修改影响了另一个对象。

拷贝时：

1.实现Cloneable接口

2.使用public访问修饰符重新定义clone方法

3.实现深拷贝的时候必须克隆所有可变域的实例域（如上代码中的hireDay域）