深入理解深、浅拷贝（Java）

​ 以下是个人理解，如有不足，请进行指正和补充，感谢您的阅读。

​ 【参考】https://cloud.tencent.com/developer/article/2158401?areaId=106001

一、什么是拷贝？

​ 拷贝（中文对copy的音译），意思是复制。复制的话，大家应该都很清楚，这里就不作详细解释，意思就是生成一个相同的事物。

​ 常见的拷贝有引用拷贝（赋值拷贝）、浅拷贝、深拷贝。

二、引用拷贝

​ 引用变量的地址，进行复制。可以理解为浅拷贝。

public static void main(String[] args) { 	    
    int a = 1; 		         
    int b = a; 	//引用拷贝，引用a的地址拷贝b。     
}

三、深拷贝和浅拷贝

​ 为了便于理解深拷贝和浅拷贝，这里先声明两个对象Student和Teacher

Student类

class Student 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; 
    }
    public Object clone() throws CloneNotSupportedException { 
         return super.clone();     
    } 
}

Teacher类

class Teacher implements Cloneable {     
    private String name;    
    private int age;    
    public Teacher(String name, int age) { 
        this.name = name; this.age = 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;   
    }
    public Object clone() throws CloneNotSupportedException { 
     return super.clone(); 
    } 
}

3.1浅拷贝

​ 仅复制当前所拷贝对象的引用地址，利用地址赋值。不包含当前所拷贝对象会引用的其他对象（称之为B），新拷贝的对象会和所拷贝的对象共享B,当B发生变化时可能会引起冲突。

public class QuoteCopy {   
    public static void main(String[] args) { 
		Teacher teacher = new Teacher(); 
        teacher.setName("张三"); 
        teacher.setAge(38);
        Student student1 = new Student(); 
        student1.setName("小明"); 
        student1.setAge(14);
        student1.setTeacher(teacher); 
    
        Student student2 = (Student) student1.clone(); //浅拷贝
        
        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()); 
        
        // 修改老师的信息 
        System.out.println("修改老师的信息后"); 
        teacher.setName("王五");
        System.out.println("student1的teacher为： " + student1.getTeacher().getName()); 
        System.out.println("student2的teacher为： " + student2.getTeacher().getName()); }
    }
} 

输出结果：

拷贝后
小明 
14
张三 
38 
修改老师的信息后
student1的teacher为：张三
student2的teacher为：张三

3.2深拷贝：

​ 复制当前所拷贝对象所包含的所有引用对象和值，生成新的地址，与原始对象独立，彼此不受影响。深拷贝相比于浅拷贝速度较慢并且花销较大。

public class DeepCopy {  
	public static void main(String[] args) throws CloneNotSupportedException {  
    Teacher teacher = new Teacher(); teacher.setName("张三");
    teacher.setAge(38); 
    Student student1 = new Student(); 
    student1.setName("苏大");
    student1.setAge(18); 
    student1.setTeacher(teacher); 
    Student student2 = (Student) student1.clone(); 
    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("小王");
    System.out.println("student1的teacher为： " + student1.getTeacher().getName()); 
    System.out.println("student2的teacher为： " + 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; 
    }
    public Object clone() throws CloneNotSupportedException { 
   		 return super.clone();
    } 
}
class Student 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; 
    } 
	public Object clone() throws CloneNotSupportedException { 
        // 浅复制时： 
        // Object object = super.clone();
        // return object;
        // 改为深复制： 
        Student student = (Student) 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((Teacher) student.getTeacher().clone()); 
        return student; }
}

输出结果:

-------------拷贝后------------- 
苏大
18
张三
38 
-------------修改老师的信息后------------- 
student1的teacher为： 张三
student2的teacher为： 小王