第五模块 为什么要使用克隆、如何实现克隆对象、序列化与反序列实现克隆的好处、深拷贝与浅拷贝

1  为什么要使用克隆

2  如何实现克隆对象

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

public class MyUtil {

    private MyUtil() {
        throw new AssertionError();
    }

    @SuppressWarnings("unchecked")
    public static <T extends Serializable> T clone(T obj) 
                                  throws Exception {
        ByteArrayOutputStream bout = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(bout);
        oos.writeObject(obj);

        ByteArrayInputStream bin = 
                    new ByteArrayInputStream(bout.toByteArray());
        ObjectInputStream ois = new ObjectInputStream(bin);
        return (T) ois.readObject();

        // 说明：调用ByteArrayInputStream
        //或ByteArrayOutputStream对象的close方法没有任何意义
        // 这两个基于内存的流只要垃圾回收器清理对象就能够释放资源，
        //这一点不同于对外部资源（如文件流）的释放
    }
}
//////////////////////////////////////
import java.io.Serializable;

/**
 * 人类
 * @author nnngu
 *
 */
class Person implements Serializable {
    private static final long serialVersionUID 
                              = -9102017020286042305L;

    private String name;    // 姓名
    private int age;        // 年龄
    private Car car;        // 座驾

    public Person(String name, int age, Car car) {
        this.name = name;
        this.age = age;
        this.car = car;
    }

    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 Car getCar() {
        return car;
    }

    public void setCar(Car car) {
        this.car = car;
    }

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

}
/////////////////////////////////////////////////////
/**
 * 小汽车类
 * @author nnngu
 *
 */
class Car implements Serializable {
    private static final long serialVersionUID 
                                = -5713945027627603702L;

    private String brand;       // 品牌
    private int maxSpeed;       // 最高时速

    public Car(String brand, int maxSpeed) {
        this.brand = brand;
        this.maxSpeed = maxSpeed;
    }

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed = maxSpeed;
    }

    @Override
    public String toString() {
        return "Car [brand=" + brand + ", 
                      maxSpeed=" + maxSpeed + "]";
    }

}
/////////////////////////////////////////////////////////////
class CloneTest {

    public static void main(String[] args) {
        try {
            Person p1 = new Person("郭靖", 33, 
                              new Car("Benz", 300));
            Person p2 = MyUtil.clone(p1);   // 深度克隆
            p2.getCar().setBrand("BYD");
            // 修改克隆的Person对象p2关联的汽车对象的品牌属性
            // 原来的Person对象p1关联的汽车不会受到任何影响
            // 因为在克隆Person对象时其关联的汽车对象也被克隆了
            System.out.println(p1);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}
//////////////////////////////////////////////////////////////

3  序列化与反序列实现克隆的好处

4 深拷贝与浅拷贝