关于Java的深拷贝和浅拷贝

1.拷贝的引入

1.1引用拷贝

创建一个指向对象的引用变量的拷贝

Teacher teacher = new Teacher("Taylor",26);
Teacher otherteacher = teacher;
System.out.println(teacher);
System.out.println(otherteacher);

输出：

blog.Teacher@355da254
blog.Teacher@355da254

由输出结果可以看出，它们的地址值是相同的，那么它们肯定是同一个对象。teacher和otherteacher的只是引用而已，他们都指向了一个相同的对象Teacher(“Taylor”,26)。 这就叫做引用拷贝。

1.2对象拷贝

创建对象本身的一个副本。

Teacher teacher = new Teacher("Swift",26);
Teacher otherteacher = (Teacher)teacher.clone();
System.out.println(teacher);
System.out.println(otherteacher);

输出：

blog.Teacher@355da254
blog.Teacher@4dc63996

由输出结果可以看出，它们的地址是不同的，也就是说创建了新的对象， 而不是把原对象的地址赋给了一个新的引用变量,这就叫做对象拷贝。

2.深拷贝与浅拷贝

在Java语言里，当我们需要拷贝一个对象时，有两种类型的拷贝：浅拷贝与深拷贝。
浅拷贝只是拷贝了源对象的地址，所以源对象的值发生变化时，拷贝对象的值也会发生变化。
而深拷贝则是拷贝了源对象的所有值，所以即使源对象的值发生变化时，拷贝对象的值也不会改变。如下图描述：

2.1浅拷贝

定义：
被复制对象的所有变量都含有与原来的对象相同的值，而所有的对其他对象的引用仍然指向原来的对象。即对象的浅拷贝会对“主”对象进行拷贝，但不会复制主对象里面的对象。"里面的对象“会在原来的对象和它的副本之间共享。

简而言之，浅拷贝仅仅复制所考虑的对象，而不复制它所引用的对象

浅拷贝实例：

public class ShallowCopy {public static void main(String[] args) throws CloneNotSupportedException {Teacher teacher = new Teacher();teacher.setName("Delacey");teacher.setAge(29);Student2 student1 = new Student2();student1.setName("Dream");student1.setAge(18);student1.setTeacher(teacher);Student2 student2 = (Student2) student1.clone();//拷贝System.out.println("拷贝后");System.out.println(student2.getName());System.out.println(student2.getAge());System.out.println(student2.getTeacher().getName());System.out.println(student2.getTeacher().getAge());System.out.println("修改老师的信息后-------------");// 修改老师的信息teacher.setName("Jam");System.out.println(student1.getTeacher().getName());System.out.println(student2.getTeacher().getName());}}class Teacher implements Cloneable {private String name;private int age;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;}
}class Student2 implements Cloneable{private String name;private int age;private Teacher teacher;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 Teacher getTeacher() {return teacher;}public void setTeacher(Teacher teacher) {this.teacher = teacher;}@Overridepublic Object clone() throws CloneNotSupportedException {Object object = super.clone();return object;}}

输出

拷贝后
Dream
18
Delacey
29
修改老师的信息后-------------
Jam
Jam

结果分析： 两个引用student1和student2指向不同的两个对象，但是两个引用student1和student2中的两个teacher引用指向的是同一个对象，所以说明是浅拷贝。

2.2深拷贝

定义：
深拷贝是一个整个独立的对象拷贝，深拷贝会拷贝所有的属性,并拷贝属性指向的动态分配的内存。当对象和它所引用的对象一起拷贝时即发生深拷贝。深拷贝相比于浅拷贝速度较慢并且花销较大。

简而言之，深拷贝把要复制的对象所引用的对象都复制了一遍。

实现深拷贝 实例1：

public class DeepCopy {public static void main(String[] args) throws Exception {Teacher2 teacher = new Teacher2();teacher.setName("Delacey");teacher.setAge(29);Student3 student1 = new Student3();student1.setName("Dream");student1.setAge(18);student1.setTeacher(teacher);Student3 student2 = (Student3) student1.clone();//拷贝System.out.println("拷贝后");System.out.println(student2.getName());System.out.println(student2.getAge());System.out.println(student2.getTeacher().getName());System.out.println(student2.getTeacher().getAge());System.out.println("修改老师的信息后-------------");// 修改老师的信息teacher.setName("Jam");System.out.println(student1.getTeacher().getName());System.out.println(student2.getTeacher().getName());}
}class Teacher2 implements Cloneable {private String name;private int age;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;}@Overridepublic Object clone() throws CloneNotSupportedException {return super.clone();}}class Student3 implements Cloneable {private String name;private int age;private Teacher2 teacher;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 Teacher2 getTeacher() {return teacher;}public void setTeacher(Teacher2 teacher) {this.teacher = teacher;}@Overridepublic Object clone() throws CloneNotSupportedException {// 浅复制时：// Object object = super.clone();// return object;// 改为深复制：Student3 student = (Student3) super.clone();// 本来是浅复制，现在将Teacher对象复制一份并重新set进来student.setTeacher((Teacher2) student.getTeacher().clone());return student;}}

输出结果：

拷贝后
Dream
18
Delacey
29
修改老师的信息后-------------
Jam
Delacey

结果分析：
两个引用student1和student2指向不同的两个对象，两个引用student1和student2中的两个teacher引用指向的是两个对象，但对teacher对象的修改只能影响student1对象,所以说是深拷贝。

下图为 teacher姓名Delacey更改前：

下图为 teacher姓名Jam更改后：

利用序列化实现深拷贝：

public class DeepCopyServiable {public static void main(String[] args) throws Exception {Teacher3 t = new Teacher3();t.setName("Taylor");t.setAge(28);Student3 s1 = new Student3();s1.setAge(20);s1.setName("blank space");s1.setTeacher(t);Student3 s2 = (Student3) s1.deepClone();//拷贝System.out.println("拷贝后:");System.out.println(s2.getName());System.out.println(s2.getAge());System.out.println(s2.getTeacher().getName());System.out.println(s2.getTeacher().getAge());System.out.println("---------------------------");t.setName("swift");System.out.println("修改后：");System.out.println(s1.getTeacher().getName());System.out.println(s2.getTeacher().getName());}
}class Teacher3 implements Serializable {private String name;private int age;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;}}class Student3 implements Serializable {private String name;private int age;private Teacher3 teacher;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 Teacher3 getTeacher() {return teacher;}public void setTeacher(Teacher3 teacher) {this.teacher = teacher;}public Object deepClone() throws Exception {// 序列化ByteArrayOutputStream bos = new ByteArrayOutputStream();ObjectOutputStream oos = new ObjectOutputStream(bos);oos.writeObject(this);// 反序列化ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());ObjectInputStream ois = new ObjectInputStream(bis);return ois.readObject();}
}

输出结果

拷贝后:
blank space
20
Taylor
28
---------------------------
修改后：
swift
Taylor

结果分析：说明用序列化的方式实现了对象的深拷贝

参考博文（侵删）：
https://blog.csdn.net/baiye_xing/article/details/71788741
https://www.cnblogs.com/ysocean/p/8482979.html
https://www.cnblogs.com/xinruyi/p/11537963.html