详解java中的深拷贝和浅拷贝（clone()方法的重写、使用序列化实现真正的深拷贝）

public class CloneUtils {

  @SuppressWarnings("unchecked")
  public static <T extends Serializable> T clone(T object){

    T cloneObj = null;
    try {
      ByteArrayOutputStream out = new ByteArrayOutputStream();
      ObjectOutputStream obs = new ObjectOutputStream(out);
      obs.writeObject(object);
      obs.close();

      ByteArrayInputStream ios = new ByteArrayInputStream(out.toByteArray());
      ObjectInputStream ois = new ObjectInputStream(ios);
      cloneObj = (T) ois.readObject();



    }catch (Exception e){
      e.printStackTrace();
    }
    return cloneObj;

  }

}

public class TestString {
  public static void main(String[] args) {
    TestString test = new TestString();
    System.out.println("-------浅拷贝---------");
    test.qianCopyTest();

    System.out.println();

    System.out.println("--------使用clone深拷贝--------");
    test.defaultCloneTest();

    System.out.println();

    System.out.println("--------使用序列化实现对象的拷贝--------");
    test.streamClonrTest();


    System.out.println("--------耗时对比--------");
    System.out.println("耗时1 : "+ test.qianCopyCost());
    System.out.println("耗时2 : "+ test.CloneCopyCost());
    System.out.println("耗时3 : "+ test.StreamCopyCost());
  }

  /*浅拷贝*/
  private void qianCopyTest() {
    String s = "cd";
    change(s);
    System.out.println(s);
    System.out.println("----------------");
    String b = new String("cd");
    change(b);
    System.out.println(b);
    System.out.println("----------------");
    int me = 1;
    change(me);
    System.out.println(me);
    System.out.println("----------------");
    Person person = new Person("我", 13,new Email("我"));
    change(person);
    System.out.println(person.toString());
  }

  /*使用默认的clone方法，需要Person实现Cloneable接口*/
  private void defaultCloneTest(){
    Person person = new Person("我", 13,new Email("我"));
    Person person1 = person.clone();
    Person person2 = person.clone();
    System.out.println("person : 【"+person+"】");
    System.out.println("person1 : 【"+person1+"】");
    System.out.println("person2 : 【"+person2+"】");
    //改一个就会触动全部！！ 这就是使用默认的clone方法的弊端
    /*该clone()方法是使用Object类的clone()方法，但是该方法存在一个缺陷，它并不会将对象的所有属性全部拷贝过来，而是有选择性的拷贝，基本规则如下：
       1、 基本类型
         如果变量是基本很类型，则拷贝其值，比如int、float等。
       2、 对象
         如果变量是一个实例对象，则拷贝其地址引用，也就是说此时新对象与原来对象是公用该实例变量。
       3、 String字符串
         若变量为String字符串，则拷贝其地址引用。但是在修改时，它会从字符串池中重新生成一个新的字符串，原有紫都城对象保持不变。*/
    person.getEmail().setContent("你");
    System.out.println("之后的person : 【"+person+"】");
    System.out.println("之后的person1 : 【"+person1+"】");
    System.out.println("之后的person2 : 【"+person2+"】");
  }

  /*使用序列化实现对象的拷贝，需要对象以及对象中的其他对象都要实现Serializable接口*/
  private void streamClonrTest(){
    Person person = new Person("我", 13,new Email("我"));
    Person person1 = CloneUtils.clone(person);
    Person person2 = CloneUtils.clone(person);
    System.out.println("person : 【"+person+"】");
    System.out.println("person1 : 【"+person1+"】");
    System.out.println("person2 : 【"+person2+"】");
    person.getEmail().setContent("你");
    System.out.println("之后的person : 【"+person+"】");
    System.out.println("之后的person1 : 【"+person1+"】");
    System.out.println("之后的person2 : 【"+person2+"】");
  }

  private static void change(String x) {
    x = "ab";
  }

  private static void change(int x) {
    x = 2;
  }

  private static void change(Person x) {
    x = new Person("你", 20, new Email("你"));
  }

  private long qianCopyCost(){
    long start = System.currentTimeMillis();
    Person person = new Person("我", 13,new Email("我"));
    List<Person> list = new ArrayList<>();
    for(int i = 0;i<=10000;i++){
      list.add(new Person("你", 20, new Email("你")));
    }
    return System.currentTimeMillis()-start;
  }

  private long CloneCopyCost(){
    long start = System.currentTimeMillis();
    Person person = new Person("我", 13,new Email("我"));
    List<Person> list = new ArrayList<>();
    for(int i = 0;i<=10000;i++){
      list.add(person.clone());
    }
    return System.currentTimeMillis()-start;
  }

  private long StreamCopyCost(){
    long start = System.currentTimeMillis();
    Person person = new Person("我", 13,new Email("我"));
    List<Person> list = new ArrayList<>();
    for(int i = 0;i<=10000;i++){
      list.add(CloneUtils.clone(person));
    }
    return System.currentTimeMillis()-start;
  }

}

class Person implements Serializable, Cloneable {

  private static final long serialVersionUID = -8584225043397465132L;
  private String name;
  private int age;

  public void setEmail(Email email) {
    this.email = email;
  }

  private Email email;

  public Email getEmail() {
    return email;
  }

  public void setName(String name) {
    this.name = name;
  }

  public void setAge(int age) {
    this.age = age;
  }

  public Person(String name, int age, Email email) {
    this.name = name;
    this.age = age;
    this.email = email;
  }

  @Override
  public String toString() {
    return "name : " + name + " | age : " + age +" | content : "+email.getContent();
  }

  @Override
  protected Person clone() {
    Person person = null;
    try {
      person = (Person) super.clone();
      /*如果加上下一行 “使用clone深拷贝” 就不会改一处其他都改变了*/
      person.setEmail(new Email(person.getEmail().getContent()));
    } catch (CloneNotSupportedException e) {
      e.printStackTrace();
    }

    return person;
  }
}

class Email implements Serializable {

  private static final long serialVersionUID = 1426052929769365539L;
  private String content;

  public void setContent(String content) {
    this.content = content;
  }

  public String getContent() {
    return content;
  }

  public Email(String content) {
    this.content = content;
  }
}