Java基础五：浅clone和深clone

一、概念

java里的clone分为：

A: 浅复制（浅克隆）: 浅复制仅仅复制所考虑的对象，还有复制对象里面的引用，而不复制它所引用的对象。

B: 深复制（深克隆）：深复制把要复制的对象所引用的对象和数组都复制了一遍。

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类的clone()方法。必须要遵循下面三点

1.在派生类中覆盖基类的clone()方法，并声明为public【Object类中的clone()方法为protected的】。

2.在派生类中实现Cloneable接口。

3.在派生类的重写clone()方法，调用super.clone()。

Object类里的clone方法是浅复制（浅克隆）

二、例子

1.浅克隆

类1：

class Teacher {
public int age;
public String name;

public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}

}

类2：

class Student implements Cloneable{

public int age ;
public String name;
public Teacher teacher;
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Teacher getTeacher() {
return teacher;
}
public void setTeacher(Teacher teacher) {
this.teacher = teacher;
}
@Override
public Object clone() throws CloneNotSupportedException {
return super.clone();
}

}

主类：

public class CloneTest {

public static void main(String[] args) throws Exception{
//teacher对象将被clone出来的Student对象共享.
Teacher teacher = new Teacher();
teacher.setAge(40);
teacher.setName("Teacher zhang");

Student student1 = new Student();
student1.setAge(20);
student1.setName("zhangsan");
student1.setTeacher(teacher);

//复制出来一个对象student2
Student student2 = (Student)student1.clone();
System.out.println(student2.getAge());
System.out.println(student2.getName());

System.out.println("~~~~~~~~~~~~~~~~~~~~~~");
System.out.println(student1.getTeacher().getAge());
System.out.println(student1.getTeacher().getName());

//修改student2的引用对象
student2.getTeacher().setAge(50);
student2.getTeacher().setName("Teacher Li");

System.out.println("~~~~~~~~~~~~~~~~~~~~~~");
System.out.println(student1.getTeacher().getAge());
System.out.println(student1.getTeacher().getName());
}
}

输出结果为：

20
zhangsan
~~~~~~~~~~~~~~~~~~~~~~
40
Teacher zhang
~~~~~~~~~~~~~~~~~~~~~~
50
Teacher Li

修改student2的teacher对象里面的age和name，发现student1的teacher的属性也发生改变，说明在clone的时候，只clone了student1中teacher对象的引用（存在栈中的），并没有clone teacher对象（存在堆中），所以student1和student2的teacher指向的是同一个对象。

2.深克隆

类1：

public int age;
public String name;

public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public Object clone() throws CloneNotSupportedException {
return super.clone();

}

}

类2：

class Student implements Cloneable{

public int age ;
public String name;
public Teacher teacher;
public int[] table;

public void setTable(int[] table)
{
this.table = table;
}

public int[] getTable()
{
return this.table;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Teacher getTeacher() {
return teacher;
}
public void setTeacher(Teacher teacher) {
this.teacher = teacher;
}
@Override
public Object clone() throws CloneNotSupportedException {
Student student = (Student)super.clone();
//将引用的对象teacher也clone下
student.setTeacher((Teacher)(student.getTeacher().clone()));
//将数组也clone一下
student.setTable(getTable().clone());
return student;
}
}

主类：

//深clone
public class DeepCloneTest {

public static void main(String[] args) throws Exception{
//teacher对象将不被clone出来的Student对象共享.
Teacher teacher = new Teacher();
teacher.setAge(40);
teacher.setName("Teacher zhang");

Student student1 = new Student();
student1.setAge(20);
student1.setName("zhangsan");
student1.setTeacher(teacher);

//复制出来一个对象student2
Student student2 = (Student)student1.clone();
System.out.println(student2.getAge());
System.out.println(student2.getName());

System.out.println("~~~~~~~~~~~~~~~~~~~~~~");
System.out.println(student1.getTeacher().getAge());
System.out.println(student1.getTeacher().getName());

//修改student2的引用对象
student2.getTeacher().setAge(50);
student2.getTeacher().setName("Teacher Li");

System.out.println("~~~~~~~~~~~~~~~~~~~~~~");
System.out.println(student1.getTeacher().getAge());
System.out.println(student1.getTeacher().getName());
}
}

输出结果为：

20
zhangsan
~~~~~~~~~~~~~~~~~~~~~~
40
Teacher zhang
~~~~~~~~~~~~~~~~~~~~~~
40
Teacher zhang

三、利用序列化做深clone

利用序列化来做深复制,把对象写到流里的过程是序列化（Serilization）过程，而把对象从流中读出来的过程则叫做反序列化（Deserialization）过程。应当指出的是，写在流里的是对象的一个拷贝，而原对象仍然存在于JVM里面。，利用这个特性，可以做深拷贝

类1：

class Teacher implements Serializable{

private static final long serialVersionUID = -8834559347461591191L;

public int age;
public String name;

public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}

}

类2：

class Student implements Serializable{

//serialVersionUID 如果你的对象序列化后存到硬盘上面后，可是后来你却更改了类的field(增加或减少或改名)，当你反序列化时，就会出现Exception的，这样就会造成不兼容性的问题。
//但当serialVersionUID相同时，它就会将不一样的field以type的缺省值赋值(如int型的是0,String型的是null等)，这个可以避开不兼容性的问题。所以最好给serialVersionUID赋值
private static final long serialVersionUID = 7991552226614088458L;

public int age ;
public String name;
public Teacher teacher;
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Teacher getTeacher() {
return teacher;
}
public void setTeacher(Teacher teacher) {
this.teacher = teacher;
}

public Object deepCopy() throws Exception{
//将该对象序列化成流,因为写在流里的是对象的一个拷贝，而原对象仍然存在于JVM里面。所以利用这个特性可以实现对象的深拷贝
ByteArrayOutputStream bos = new ByteArrayOutputStream();

ObjectOutputStream oos = new ObjectOutputStream(bos);

oos.writeObject(this);

//将流序列化成对象
ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());

ObjectInputStream ois = new ObjectInputStream(bis);

return ois.readObject();
}

}

主类：

//利用序列化来做深复制
//深clone
public class DeepCloneTest {

public static void main(String[] args) throws Exception{
//teacher对象将不被clone出来的Student对象共享.
Teacher teacher = new Teacher();
teacher.setAge(40);
teacher.setName("Teacher zhang");

Student student1 = new Student();
student1.setAge(20);
student1.setName("zhangsan");
student1.setTeacher(teacher);

//复制出来一个对象student2
Student student2 = (Student)student1.deepCopy();
System.out.println(student2.getAge());
System.out.println(student2.getName());

System.out.println("~~~~~~~~~~~~~~~~~~~~~~");
System.out.println(student1.getTeacher().getAge());
System.out.println(student1.getTeacher().getName());

//修改student2的引用对象
student2.getTeacher().setAge(50);
student2.getTeacher().setName("Teacher Li");

System.out.println("~~~~~~~~~~~~~~~~~~~~~~");
System.out.println(student1.getTeacher().getAge());
System.out.println(student1.getTeacher().getName());
}
}

输出结果为：

20
zhangsan
~~~~~~~~~~~~~~~~~~~~~~
40
Teacher zhang
~~~~~~~~~~~~~~~~~~~~~~
40
Teacher zhang