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Java对象复制

由 五迷三道 提交于 2019-12-09 09:51:08

1.Java对象复制概念

    1.1 浅复制（浅克隆）

        复制的对象的所有变量与含有与原来的对象相同的值，而所有的对其他对象的引用仍然指向原对象。换言之，浅复制仅仅复制所考虑的对象，而不复制它所引用的对象。

    1.2 深复制（深度克隆）

        复制的对象的所有变量都含有与原来的对象相同的值，除去那些引用其他对象的变量。那些引用其他对象的变量将指向复制的新对象，而不是原来的对象。换言之，深复制把要复制的对象所引用的对象都复制了一遍。

2.Java对象的clone()克隆方法

    2.1 clone方法

    clone方法将对象复制了一份并返回给调用者。一般而言，clone()方法满足

  • 对任何的对象x，都有x.clone() != x;也即克隆的对象与原对象不是同一个对象，他们有不同的内存地址
  • 对任何的对象x，都有x.clone().getClass() == x.getClass()，也即克隆对象与原对象的类型一致。
  • 如果对象x的equals()方法定义恰当，那么x.clone().equal(x)应该成立。

    2.2 Java中对象的克隆

  • 为了获取对象的一份拷贝，我们可以利用Object的clone()方法
  • 在派生类中覆盖基类的clone()方法，并声明为public
  • 在派生类的clone()方法中，调用super.clone()。
  • 在派生类中实现Cloneable接口

    2.3 示例

    2.3.1 浅复制示例

package org.wem.im;

/**
 * 
 * <p>
 * Title: Person<br>
 * Copyright: Copyright (c) 2016<br>
 * Company: <br>
 * </p>
 *
 * <p>
 * Description: 测试Java对象浅克隆
 * </p>
 *
 * @version v1.0.0
 * @author kucs
 * @date 2016年9月30日下午2:28:22
 *
 * Modification History:
 *---------------------------------------------------------*
 *
 */
public class Person implements Cloneable {
	class Worker{
		private String workName;
		private String department;
		public String getWorkName() {
			return workName;
		}
		public void setWorkName(String workName) {
			this.workName = workName;
		}
		public String getDepartment() {
			return department;
		}
		public void setDepartment(String department) {
			this.department = department;
		}
		@Override
		public String toString() {
			return "Worker [workName=" + workName + ", department=" + department + "]";
		}
		
	}
	private String name;
	private String age;
	private String weight;
	private String height;
	private Worker worker;
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getAge() {
		return age;
	}
	public void setAge(String age) {
		this.age = age;
	}
	public String getWeight() {
		return weight;
	}
	public void setWeight(String weight) {
		this.weight = weight;
	}
	public String getHeight() {
		return height;
	}
	public void setHeight(String height) {
		this.height = height;
	}
	
	public Worker getWorker() {
		return worker;
	}
	public void setWorker(Worker worker) {
		this.worker = worker;
	}
	@Override
	protected Object clone() throws CloneNotSupportedException {
		// TODO Auto-generated method stub
		return super.clone();
	}
	
	@Override
	public String toString() {
		return "Person [name=" + name + ", age=" + age + ", weight=" + weight + ", height=" + height + ", worker="
				+ worker + "]";
	}
	public static void main(String[] args) throws CloneNotSupportedException {
		Person p = new Person();
		Worker worker = p.new Worker();
		worker.setWorkName("asiainfo");
		worker.setDepartment("cboss");
		p.setWorker(worker);
		p.setName("kucs");
		p.setAge("24");
		p.setWeight("65");
		p.setHeight("170");
		Person p_clone = (Person) p.clone();
		System.out.println("原对象信息："+p.toString());
		System.out.println("克隆对象信息："+p_clone.toString());
		//修改p_clone对象的值
		p_clone.setName("kucs_clone");
		//修改对象引用的对象的值
		worker.setWorkName("asianinfo_clone");
		System.out.println("修改后的克隆对象信息："+p_clone.toString());
		System.out.println("原对象信息："+p.toString());
		if(p.getWorker().getWorkName().equals(p_clone.getWorker().getWorkName())){
			System.out.println("浅复制对象，其引用的对象未复制");
		}else{
			System.out.println("非浅复制对象，其引用的对象也复制");
		}
	}
}

运行结果

原对象信息：Person [name=kucs, age=24, weight=65, height=170, worker=Worker [workName=asiainfo, department=cboss]]
克隆对象信息：Person [name=kucs, age=24, weight=65, height=170, worker=Worker [workName=asiainfo, department=cboss]]
修改后的克隆对象信息：Person [name=kucs_clone, age=24, weight=65, height=170, worker=Worker [workName=asianinfo_clone, department=cboss]]
原对象信息：Person [name=kucs, age=24, weight=65, height=170, worker=Worker [workName=asianinfo_clone, department=cboss]]
浅复制对象，其引用的对象未复制

结果说明：浅克隆之后的对象与原对象不是同一个对象。修改其中一个对象的值对另一个对象没有影响。

                浅克隆中其引用的对象未复制，还是指向同一个对象。

    2.3.2 深复制示例

        对浅复制示例代码做了调整

package org.wem.im;

/**
 * 
 * <p>
 * Title: Person<br>
 * Copyright: Copyright (c) 2016<br>
 * Company: <br>
 * </p>
 *
 * <p>
 * Description: 测试Java对象深度克隆
 * </p>
 *
 * @version v1.0.0
 * @author kucs
 * @date 2016年9月30日下午2:45:22
 *
 * Modification History:
 *---------------------------------------------------------*
 *
 */
public class Person implements Cloneable {
	class Worker implements Cloneable{
		private String workName;
		private String department;
		public String getWorkName() {
			return workName;
		}
		public void setWorkName(String workName) {
			this.workName = workName;
		}
		public String getDepartment() {
			return department;
		}
		public void setDepartment(String department) {
			this.department = department;
		}
		
		@Override
		protected Object clone() throws CloneNotSupportedException {
			// TODO Auto-generated method stub
			return super.clone();
		}
		@Override
		public String toString() {
			return "Worker [workName=" + workName + ", department=" + department + "]";
		}
		
	}
	private String name;
	private String age;
	private String weight;
	private String height;
	private Worker worker;
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getAge() {
		return age;
	}
	public void setAge(String age) {
		this.age = age;
	}
	public String getWeight() {
		return weight;
	}
	public void setWeight(String weight) {
		this.weight = weight;
	}
	public String getHeight() {
		return height;
	}
	public void setHeight(String height) {
		this.height = height;
	}
	
	public Worker getWorker() {
		return worker;
	}
	public void setWorker(Worker worker) {
		this.worker = worker;
	}
	@Override
	protected Object clone() throws CloneNotSupportedException {
		// TODO Auto-generated method stub
		Person p = (Person) super.clone();
		p.worker = (Worker) worker.clone();
		return p;
	}
	
	@Override
	public String toString() {
		return "Person [name=" + name + ", age=" + age + ", weight=" + weight + ", height=" + height + ", worker="
				+ worker + "]";
	}
	public static void main(String[] args) throws CloneNotSupportedException {
		Person p = new Person();
		Worker worker = p.new Worker();
		worker.setWorkName("asiainfo");
		worker.setDepartment("cboss");
		p.setWorker(worker);
		p.setName("kucs");
		p.setAge("24");
		p.setWeight("65");
		p.setHeight("170");
		Person p_clone = (Person) p.clone();
		System.out.println("原对象信息："+p.toString());
		System.out.println("克隆对象信息："+p_clone.toString());
		//修改p_clone对象的值
		p_clone.setName("kucs_clone");
		//修改对象引用的对象的值
		worker.setWorkName("asianinfo_clone");
		System.out.println("修改后的克隆对象信息："+p_clone.toString());
		System.out.println("原对象信息："+p.toString());
		if(p.getWorker().getWorkName().equals(p_clone.getWorker().getWorkName())){
			System.out.println("浅复制对象，其引用的对象未复制");
		}else{
			System.out.println("非浅复制对象，其引用的对象也复制");
		}
	}
}

    运行结果：

原对象信息：Person [name=kucs, age=24, weight=65, height=170, worker=Worker [workName=asiainfo, department=cboss]]
克隆对象信息：Person [name=kucs, age=24, weight=65, height=170, worker=Worker [workName=asiainfo, department=cboss]]
修改后的克隆对象信息：Person [name=kucs_clone, age=24, weight=65, height=170, worker=Worker [workName=asiainfo, department=cboss]]
原对象信息：Person [name=kucs, age=24, weight=65, height=170, worker=Worker [workName=asianinfo_clone, department=cboss]]
非浅复制对象，其引用的对象也复制

    结果说明：深克隆中，对克隆后的对象修改值，不影响原对象的值。修改克隆后的对象引用的值，对原对象引用的对象也没有影响。

3.利用串行化来做深复制

    这主要是为了避免重写比较复杂的深复制clone()方法。把对象写到流里的过程是串行化过程（Serialization），把对象从流中读取出来是并行化（Deserialization）过程。

    注意：写在流里的对象时一个拷贝，而原对象仍然存在jvm中，因此串行化过程只是一个对象的拷贝。

    在Java语言中，深复制一个对象，常常可以先使用对象实现Serializable接口，然后把对象写到一个流里，再从流里读取出来，便可以重建对象。

package org.wem.im;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;

/**
 * 
 * <p>
 * Title: Person<br>
 * Copyright: Copyright (c) 2016<br>
 * Company: <br>
 * </p>
 *
 * <p>
 * Description: 测试Java对象克隆
 * </p>
 *
 * @version v1.0.0
 * @author kucs
 * @date 2016年9月30日下午2:28:22
 *
 * Modification History:
 *---------------------------------------------------------*
 *
 */
public class Person implements Serializable {
	class Worker implements Serializable{
		private String workName;
		private String department;
		public String getWorkName() {
			return workName;
		}
		public void setWorkName(String workName) {
			this.workName = workName;
		}
		public String getDepartment() {
			return department;
		}
		public void setDepartment(String department) {
			this.department = department;
		}
		
		@Override
		public String toString() {
			return "Worker [workName=" + workName + ", department=" + department + "]";
		}
		
	}
	private String name;
	private String age;
	private String weight;
	private String height;
	private Worker worker;
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getAge() {
		return age;
	}
	public void setAge(String age) {
		this.age = age;
	}
	public String getWeight() {
		return weight;
	}
	public void setWeight(String weight) {
		this.weight = weight;
	}
	public String getHeight() {
		return height;
	}
	public void setHeight(String height) {
		this.height = height;
	}
	
	public Worker getWorker() {
		return worker;
	}
	public void setWorker(Worker worker) {
		this.worker = worker;
	}
	public Object deepClone() throws IOException, ClassNotFoundException{
		//将对象写到流
		ByteArrayOutputStream bo = new ByteArrayOutputStream();
		ObjectOutputStream oo = new ObjectOutputStream(bo);
		oo.writeObject(this);
		//从流里读取处理啊
		ByteArrayInputStream bi = new ByteArrayInputStream(bo.toByteArray());
		ObjectInputStream oi = new ObjectInputStream(bi);
		return oi.readObject();
	}
	@Override
	public String toString() {
		return "Person [name=" + name + ", age=" + age + ", weight=" + weight + ", height=" + height + ", worker="
				+ worker + "]";
	}
	public static void main(String[] args) throws CloneNotSupportedException, ClassNotFoundException, IOException {
		Person p = new Person();
		Worker worker = p.new Worker();
		worker.setWorkName("asiainfo");
		worker.setDepartment("cboss");
		p.setWorker(worker);
		p.setName("kucs");
		p.setAge("24");
		p.setWeight("65");
		p.setHeight("170");
		Person p_clone = (Person) p.deepClone();
		System.out.println("原对象信息："+p.toString());
		System.out.println("克隆对象信息："+p_clone.toString());
		//修改p_clone对象的值
		p_clone.setName("kucs_clone");
		//修改对象引用的对象的值
		worker.setWorkName("asianinfo_clone");
		System.out.println("修改后的克隆对象信息："+p_clone.toString());
		System.out.println("原对象信息："+p.toString());
		if(p.getWorker().getWorkName().equals(p_clone.getWorker().getWorkName())){
			System.out.println("浅复制对象，其引用的对象未复制");
		}else{
			System.out.println("非浅复制对象，其引用的对象也复制");
		}
	}
}

运行结果

原对象信息：Person [name=kucs, age=24, weight=65, height=170, worker=Worker [workName=asiainfo, department=cboss]]
克隆对象信息：Person [name=kucs, age=24, weight=65, height=170, worker=Worker [workName=asiainfo, department=cboss]]
修改后的克隆对象信息：Person [name=kucs_clone, age=24, weight=65, height=170, worker=Worker [workName=asiainfo, department=cboss]]
原对象信息：Person [name=kucs, age=24, weight=65, height=170, worker=Worker [workName=asianinfo_clone, department=cboss]]
非浅复制对象，其引用的对象也复制

 

标签
java
克隆
clone
深复制
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