Java克隆--深克隆与浅克隆的区别

  克隆，就是复制一个对象的副本，而克隆又分浅克隆和深克隆。浅克隆是指克隆得到的对象基本类型的值改变了，而源对象的值不会变。但如果被克隆对象引用类型的值改变了，那么源对象的值同样会改变，因为引用类型在栈内存中存放的是一个引用地址，被克隆对象后也和源对象的引用地址一样，都是指向同样的内存空间的值。所以在克隆时，任何一个对象的值的改变都会令另外的值改变，所以这种情况下要用深克隆。

  要注意的是要克隆的对象的泪必须继承cloneable接口。浅克隆的特点是只克隆该对象本体，它的优缺点就是一改皆改；深克隆的特点是新建对象，与源对象互不干扰，而它的优缺点也是互不干扰和麻烦。通常情况下我们使用克隆的时候都只使用浅克隆。

  对克隆可以简单的理解为：当克隆一个对象时，把属性的值和方法都一起拷贝的是浅拷贝，而方法的值可以设置不同的是深克隆。深克隆要进行反序例化，先把内容输出到内存，再从内存读取。

浅克隆：

package com.lk.B;

public class Address {
	private String state;
	private String province;
	private String city;
	public Address(String state,String province,String city){
		this.state = state;
		this.province = province;
		this.city = city;
	}
	public String getState() {
		return state;
	}
	public void setState(String state) {
		this.state = state;
	}
	public String getProvince() {
		return province;
	}
	public void setProvince(String province) {
		this.province = province;
	}
	public String getCity() {
		return city;
	}
	public void setCity(String city) {
		this.city = city;
	}
	@Override
	public String toString() {
		// TODO Auto-generated method stub
		StringBuffer sb = new StringBuffer();
		sb.append("国家："+this.state+",");
		sb.append("省："+this.province+",");
		sb.append("市："+this.city);
		return sb.toString();
	}
}

　　

package com.lk.B;

public class Employees implements Cloneable{
	private String name;
	private int age;
	private Address address;
	public Employees(String name,int age,Address address){
		this.name = name;
		this.age = age;
		this.address = address;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	public Address getAddress() {
		return address;
	}
	public void setAddress(Address address) {
		this.address = address;
	}
	@Override
	public String toString() {
		// TODO Auto-generated method stub
		StringBuffer sb = new StringBuffer();
		sb.append("姓名:"+name+",");
		sb.append("年龄:"+age+"
");
		sb.append("地址"+address);
		return sb.toString();
	}
	@Override
	protected Employees clone() {//原本返回值应该是Object，但是这里返回的是Employees，为协变类型
		                         //即子类覆盖（即重写）基类方法时，返回的类型可以是基类方法返回类型的子类。
		// TODO Auto-generated method stub
		Employees employee = null;
		
		try {
			employee = (Employees) super.clone();
		} catch (CloneNotSupportedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return employee;
	}
}

　　

package com.lk.B;

public class Test2 {

	public static void main(String[] args) {//此方法并没有克隆成功，原因是对于引用类型不能使用浅克隆
		// TODO Auto-generated method stub
		System.out.println("克隆之前：");
		Address address = new Address("中国", "黑龙江", "哈尔滨");
		Employees employee1 = new Employees("阿坤", 21, address);
		System.out.println("员工1的信息：");
		System.out.println(employee1);
		System.out.println("克隆之后:");
		Employees employee2 = employee1.clone();
		employee2.getAddress().setState("中国");
		employee2.getAddress().setProvince("上海");
		employee2.getAddress().setCity("杨浦");
		employee2.setName("lk");
		employee2.setAge(22);
		System.out.println("员工2的信息：");
		System.out.println(employee2);
		System.out.println("员工1的信息：");
		System.out.println(employee1);
	}

}

　　输出：

/*
   克隆之前：
员工1的信息：
姓名:阿坤,年龄:21
地址国家：中国,省：黑龙江,市：哈尔滨
克隆之后:
员工2的信息：
姓名:lk,年龄:22
地址国家：杨浦,省：上海,市：哈尔滨
员工1的信息：
姓名:阿坤,年龄:21
地址国家：杨浦,省：上海,市：杨浦
*/

　　

此时并没有克隆成功，因为对于引用类型不能使用浅克隆，需要使用深克隆

实现深克隆有两种方法，这里先介绍第一种方法：一次克隆各个可变的引用类型：即只要有类中包含了引用类型就将那个引用类型进行克隆，在这个例子里，即需要对Address类也需要克隆，由于Address中都是基本类型（String在这里我先叫做基本类型，因为String比较特殊）

深克隆：

package com.lk.B;

public class Address implements Cloneable{
	private String state;
	private String province;
	private String city;
	public Address(String state,String province,String city){
		this.state = state;
		this.province = province;
		this.city = city;
	}
	public String getState() {
		return state;
	}
	public void setState(String state) {
		this.state = state;
	}
	public String getProvince() {
		return province;
	}
	public void setProvince(String province) {
		this.province = province;
	}
	public String getCity() {
		return city;
	}
	public void setCity(String city) {
		this.city = city;
	}
	@Override
	public String toString() {
		// TODO Auto-generated method stub
		StringBuffer sb = new StringBuffer();
		sb.append("国家："+this.state+",");
		sb.append("省："+this.province+",");
		sb.append("市："+this.city);
		return sb.toString();
	}
	@Override
	protected Address clone() {
		// TODO Auto-generated method stub
		Address address = null;
		try {
			address = (Address) super.clone();
		} catch (CloneNotSupportedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return address;
	}
}

　　

package com.lk.B;

public class Employees implements Cloneable{
	private String name;
	private int age;
	private Address address;
	public Employees(String name,int age,Address address){
		this.name = name;
		this.age = age;
		this.address = address;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	public Address getAddress() {
		return address;
	}
	public void setAddress(Address address) {
		this.address = address;
	}
	@Override
	public String toString() {
		// TODO Auto-generated method stub
		StringBuffer sb = new StringBuffer();
		sb.append("姓名:"+name+",");
		sb.append("年龄:"+age+"
");
		sb.append("地址"+address);
		return sb.toString();
	}
	@Override
	protected Employees clone() {//原本返回值应该是Object，但是这里返回的是Employees，为协变类型
		                         //即子类覆盖（即重写）基类方法时，返回的类型可以是基类方法返回类型的子类。
		// TODO Auto-generated method stub
		Employees employee = null;
		
		try {
			employee = (Employees) super.clone();
			employee.address = address.clone();
		} catch (CloneNotSupportedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return employee;
	}
}

　　

package com.lk.B;

public class Test2 {

	public static void main(String[] args) {//深克隆，克隆成功
		// TODO Auto-generated method stub
		System.out.println("克隆之前：");
		Address address = new Address("中国", "黑龙江", "哈尔滨");
		Employees employee1 = new Employees("阿坤", 21, address);
		System.out.println("员工1的信息：");
		System.out.println(employee1);
		System.out.println("克隆之后:");
		Employees employee2 = employee1.clone();
		employee2.getAddress().setState("中国");
		employee2.getAddress().setProvince("上海");
		employee2.getAddress().setCity("杨浦");
		employee2.setName("lk");
		employee2.setAge(22);
		System.out.println("员工2的信息：");
		System.out.println(employee2);
		System.out.println("员工1的信息：");
		System.out.println(employee1);
	}

}

　　

/*
克隆之前：
员工1的信息：
姓名:阿坤,年龄:21
地址国家：中国,省：黑龙江,市：哈尔滨
克隆之后:
员工2的信息：
姓名:lk,年龄:22
地址国家：中国,省：上海,市：杨浦
员工1的信息：
姓名:阿坤,年龄:21
地址国家：中国,省：黑龙江,市：哈尔滨

*/

　　注意：使用重写clone方法时必须要实现Cloneable接口，否则会出现：java.lang.CloneNotSupportedException异常