Java 潜拷贝和深拷贝（浅复制和深复制）

最近有学妹问到这个问题，自己在学习Java也没有注意到问题，故而又重新看了一下这部分，整理一下，也算方便大家。

首先我们看看浅拷贝和深拷贝的定义 浅拷贝：只复制一个对象，对象内部存在的指向其他对象数组或者引用则不复制。 深拷贝：对象，对象内部的引用均复制。 为了更好的理解它们的区别我们假设有一个对象A，它包含有2对象对象A1和对象A2  对象A进行浅拷贝后，得到对象B但是对象A1和A2并没有被拷贝 对象A进行深拷贝，得到对象B的同时A1和A2连同它们的引用也被拷贝

总结一下：

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.在派生类的clone()方法中，调用super.clone()。 3.在派生类中实现Cloneable接口。 

Object类里的clone方法是浅复制（浅克隆）

浅复制（浅克隆）的例子：

package com.test; //浅复制（浅克隆）: 浅复制仅仅复制所考虑的对象，而不复制它所引用的对象。 //深复制（深克隆）：深复制把要复制的对象所引用的对象都复制了一遍。 // //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.在派生类的clone()方法中，调用super.clone()。 //3.在派生类中实现Cloneable接口。 //<SPAN style="COLOR: red">Object类里的clone方法是浅复制（浅克隆）</SPAN>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()); } } 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; } } 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(); } } 输出结果为： 20 zhangsan ~~~~~~~~~~~~~~~~~~~~~~ 40 Teacher zhang ~~~~~~~~~~~~~~~~~~~~~~ 50 Teacher Li 2.深复制（深Clone）例子： 

package com.test1; //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()); } } class Teacher implements Cloneable{ 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(); } } 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 { Student student = (Student)super.clone(); //将引用的对象teacher也clone下 student.setTeacher((Teacher)(student.getTeacher().clone())); return student; } } 输出结果为： 20 zhangsan ~~~~~~~~~~~~~~~~~~~~~~ 40 Teacher zhang ~~~~~~~~~~~~~~~~~~~~~~ 40 Teacher zhang 3.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 。

package com.test3; import java.io.ByteArrayInputStream; import java.io.ByteArrayOutputStream; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; import java.io.Serializable; //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()); } } 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; } } 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(); } } 输出结果为： 20 zhangsan ~~~~~~~~~~~~~~~~~~~~~~ 40 Teacher zhang ~~~~~~~~~~~~~~~~~~~~~~ 40 Teacher zhang

转载于:https://www.cnblogs.com/ituff/archive/2012/09/24/2858519.html

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