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+"]";
	}
	
}

輸出結果：

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]

學習小結：

在對各個域進行對應的拷貝時，如果對象中包含了子對象的引用，拷貝的結果會是的兩個域引用同一個子對象

因此原始對象與拷貝對象共享這部分信息。若這部分信息不會發生改變時，則進行淺拷貝（默認拷貝）即可，但是

如果這部分信息會發生改變，那麼需要進行深拷貝，以防止一個對象對這部分信息的修改影響了另一個對象。

拷貝時：

1.實現Cloneable接口

2.使用public訪問修飾符重新定義clone方法

3.實現深拷貝的時候必須克隆所有可變域的實例域（如上代碼中的hireDay域）