java对象拷贝常见面试题及应答汇总

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();
    }
  }
}