java 浅度clone及深度clone

     被clone的对象如果有属性是引用型对象，如果不复写clone方法，则clone是浅度clone。即当被clone的对象引用的对象发生改变时，clone的对象也会相应发生改变。clone的对象与被clone的对象不能保持独立。

例如：

package hashcode;

import java.util.HashMap;
import java.util.HashSet;
import java.util.Hashtable;

/**
 * @author Administrator
 * 
 */
public class Student implements Cloneable {

	private int age;
	private String name;
	private Student deskmate;

	public Student getDeskmate() {
		return deskmate;
	}

	public void setDeskmate(Student deskmate) {
		this.deskmate = deskmate;
	}

	public int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

               @Override
	public String toString() {
                    return "Student [age=" + age + ", name=" + name + ",  deskmate="+deskmate + "]";
	}

	public Student(int age, String name) {
   		super();
		this.age = age;
		this.name = name;
	}
               public static void main(String[] args) throws CloneNotSupportedException {
		
		// clone
		Student goodStudent = new Student("goodStudent", 12);
		Student student1 = new Student("liuliu", 10);
		student1.setDeskmate(goodStudent);
		Student student2 = (Student) student1.clone();

		System.out.println(student1);
//result: Student [age=10, name=liuliu, deskmate=Student [age=12, name=goodStudent, deskmate=null]]
		System.out.println(student2);
//result: Student [age=10, name=liuliu, deskmate=Student [age=12, name=goodStudent, deskmate=null]]

		// student1's deskmate's name is changed.
		// student2 has the same reference, student2's deskmate's name is the
		// same as student 1's.
		// This is shallow clone.
		student1.getDeskmate().setName("badStudent");

		System.out.println(student1);
//result: Student [age=10, name=liuliu, deskmate=Student [age=12, name=badStudent, deskmate=null]]
		System.out.println(student2);
// Student [age=10, name=liuliu, deskmate=Student [age=12, name=badStudent, deskmate=null]]
	}

}

深度clone则需覆写clone方法：

@Override
	protected Object clone() throws CloneNotSupportedException {
		Student s = (Student) super.clone();
		Student dm = new Student();
		dm.setAge(s.getDeskmate().getAge());
		dm.setName(s.getDeskmate().getName());
		s.setDeskmate(dm);
		return s;
	}

 这样测试结果表明clone后的对象与被clone的对象是独立的

public static void main(String[] args) throws CloneNotSupportedException {


		Student goodStudent = new Student("goodStudent", 12);
		Student student1 = new Student("liuliu", 10);
		student1.setDeskmate(goodStudent);
		Student student2 = (Student) student1.clone();

		System.out.println(student1);
//result: Student [age=10, name=liuliu, deskmate=Student [age=12, name=goodStudent, deskmate=null]]
		System.out.println(student2);
//result: Student [age=10, name=liuliu, deskmate=Student [age=12, name=goodStudent, deskmate=null]]
		// student1's deskmate's name is changed.
		// student2 has its own reference
		// This is deep copy.
		student1.getDeskmate().setName("badStudent");

		System.out.println(student1);
//result: Student [age=10, name=liuliu, deskmate=Student [age=12, name=badStudent, deskmate=null]]
		System.out.println(student2);
//result: Student [age=10, name=liuliu, deskmate=Student [age=12, name=goodStudent, deskmate=null]]

}