关于Java的深拷贝和浅拷贝

深碍√TFBOYSˉ_ 2023-09-24 19:10 50阅读 0赞

### 文章目录 ###

*  1.拷贝的引入
 *   *  1.1引用拷贝
     *  1.2对象拷贝
 *  2.深拷贝与浅拷贝
 *   *  2.1浅拷贝
     *  2.2深拷贝

# 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**。  
![在这里插入图片描述][651bf4e2578f4191b3dd24f908a46208.png]

## 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**。  
![在这里插入图片描述][4042d3753f6544c2945adf1881b97a25.png]

# 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：  
![在这里插入图片描述][aedd26d8d6ae469891c6a537b9cb55c9.png]

## 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;
        }
    
        @Override
        public 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**。  
![在这里插入图片描述][99d36531a1824274a4b8fa268ca34492.png]

## 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;
        }
    
        @Override
        public 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;
        }
    
        @Override
        public 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：  
![在这里插入图片描述][7fdfc5562df140538baa1742d35429fe.png]  
下图为 teacher姓名Jam更改后：  
![在这里插入图片描述][613c58d5e0a748f5a80c3d3d38d64a8e.png]  
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

[651bf4e2578f4191b3dd24f908a46208.png]: https://img-blog.csdnimg.cn/651bf4e2578f4191b3dd24f908a46208.png
[4042d3753f6544c2945adf1881b97a25.png]: https://img-blog.csdnimg.cn/4042d3753f6544c2945adf1881b97a25.png
[aedd26d8d6ae469891c6a537b9cb55c9.png]: https://img-blog.csdnimg.cn/aedd26d8d6ae469891c6a537b9cb55c9.png
[99d36531a1824274a4b8fa268ca34492.png]: https://img-blog.csdnimg.cn/99d36531a1824274a4b8fa268ca34492.png
[7fdfc5562df140538baa1742d35429fe.png]: https://img-blog.csdnimg.cn/7fdfc5562df140538baa1742d35429fe.png
[613c58d5e0a748f5a80c3d3d38d64a8e.png]: https://img-blog.csdnimg.cn/613c58d5e0a748f5a80c3d3d38d64a8e.png