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java中的深层复制和浅层复制

浅层复制的时候,一个对象仅仅在引用另外一个对象。属性没被clone。而深层复制将属性也一并clone.

Java对象的浅层复制是指Java对象A本身被clone成新对象B,但A的属性没有被clone处理,只是把A的各个属性所指的对象赋值到B对应的属性上,A与B的相同属性都引用到同一个对象。

Java对象的深层复制是指Java对象A本身被clone成新对象B,同时A的属性也是被clone成新对象,赋值到A的各个属性上去,A与B的相同属性都引用到不同的对象;

先看一个浅层复制基本的例子

package com.javaer.examples;

import java.util.Date;

/**
 * java浅层复制的特点
 * 
 * @author mc2
 * 
 */
public class ShallowCopy {
	private String name;
	private int age;

	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;
	}

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		ShallowCopy a = new ShallowCopy();
		a.setName("yuexiaosheng");
		a.setAge(30);
		System.out.println("a name:" + a.getName());
		System.out.println("a age:" + a.getAge());
		
		ShallowCopy b = new ShallowCopy();
		b.setName(a.getName());
		b.setAge(a.getAge());
		System.out.println("b name:" + b.getName());
		System.out.println("b age:" + b.getAge());
		
		
		b.setAge(40);
		System.out.println("b name:" + b.getName());
		System.out.println("b age:" + b.getAge());
		System.out.println("a name:" + a.getName());
		System.out.println("a age:" + a.getAge());
		
		
		
		
	}

}

B的改变,不会对A造成任何影响。

如果Java对象的属性都是只读类的话,如原始数据类型、数据封装类、String、BigDecimal、BigInteger等,那么浅层复制与深层复制达到的效果是一样的。如果属性有Date或其他自定的数据类,那么线层复制,B的修改可能导致A的改变。数据就串了。

package com.javaer.examples;

import java.util.Date;

/**
 * java浅层复制的特点
 * 
 * @author mc2
 * 
 */
public class ShallowCopy implements Cloneable {
	private String name;
	private int age;
	private Date brith;
	
	public ShallowCopy clone(){
		try {
			return (ShallowCopy)super.clone();
		} catch (CloneNotSupportedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return null;
	}
	
	
	public Date getBrith() {
		return brith;
	}
	
	public void setBrith(Date brith) {
		this.brith = brith;
	}

	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;
	}

	/**
	 * @param args
	 * @throws CloneNotSupportedException 
	 */
	public static void main(String[] args) throws CloneNotSupportedException {
		ShallowCopy a = new ShallowCopy();
		a.setName("yuexiaosheng");
		a.setAge(30);
		a.setBrith(new Date());
		System.out.println("a name:" + a.getName());
		System.out.println("a age:" + a.getAge());
		System.out.println("a brith:" + a.getBrith());
		System.out.println("---------------------------------------" );
		
		ShallowCopy b = new ShallowCopy();
		b.setName(a.getName());
		b.setAge(a.getAge());
		b.setBrith(a.getBrith());
		//ShallowCopy b = (ShallowCopy) a.clone();
		System.out.println("b name:" + b.getName());
		System.out.println("b age:" + b.getAge());
		System.out.println("b brith:" + b.getBrith());
		System.out.println("---------------------------------------" );
		
		
		b.setAge(40);
	//	b.setBrith(new Date(100000L));
		b.getBrith().setTime(100000L);
		System.out.println("b name:" + b.getName());
		System.out.println("b age:" + b.getAge());
		System.out.println("b brith:" + b.getBrith());
		System.out.println("---------------------------------------" );
		
		System.out.println("a name:" + a.getName());
		System.out.println("a age:" + a.getAge());
		System.out.println("a brith:" + a.getBrith());
		System.out.println("---------------------------------------" );
		
	}

}

上面的例子,当使用b.setBrith(new Date(100000L)); 不会对A发生改变。但是如果b.getBrith().setTime(100000L);这样就会改变A

上面例子实现浅层复制办法有两个
1.ShallowCopy b = new ShallowCopy();
b.setName(a.getName());
b.setAge(a.getAge());
b.setBrith(a.getBrith());
2.ShallowCopy b = (ShallowCopy) a.clone();

那么如何实现深层复制?

将clone函数修改如下。

public ShallowCopy clone(){
		ShallowCopy T = null;
		try {
			 T = (ShallowCopy)super.clone();
			T.brith = (Date)T.brith.clone();
		} catch (CloneNotSupportedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return T;
	}

核心是增加了一个句话来clone属性
T.brith = (Date)T.brith.clone();

java数据中常见的浅层复制方式
String[] ary = {"Tom","Jerry"};

String[] ary1 = Arrays.copyOf(ary, ary.length);


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