Java深入理解深拷贝和浅拷贝区别

一、拷贝的引入

（1）、引用拷贝

创建一个指向对象的引用变量的拷贝。

public class QuoteCopy {
    public static void main(String[] args) {
        Teacher teacher = new Teacher("riemann", 28);
        Teacher otherTeacher = teacher;
        System.out.println(teacher);
        System.out.println(otherTeacher);
    }
}

class Teacher {
    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;
    }
}

输出结果：

com.test.Teacher@28a418fc
com.test.Teacher@28a418fc

结果分析：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(“riemann”,28)。 这就叫做引用拷贝。

 

（2）、对象拷贝

创建对象本身的一个副本。

public class ObjectCopy {
    public static void main(String[] args) throws CloneNotSupportedException {
        Teacher teacher = new Teacher("riemann", 28);
        Teacher otherTeacher = (Teacher) teacher.clone();
        System.out.println(teacher);
        System.out.println(otherTeacher);
    }
}

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 {
        Object object = super.clone();
        return object;
    }
}

输出结果：

com.test.Teacher@28a418fc
com.test.Teacher@5305068a

结果分析：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。

 注：深拷贝和浅拷贝都是对象拷贝

二、浅拷贝

（1）、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。

（2）、浅拷贝实例

public class ShallowCopy {
    public static void main(String[] args) throws CloneNotSupportedException {
        Teacher teacher = new Teacher();
        teacher.setName("riemann");
        teacher.setAge(28);

        Student student1 = new Student();
        student1.setName("edgar");
        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("jack");
        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;
    }
}

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 {
        Object object = super.clone();
        return object;
    }
}

输出结果：

-------------拷贝后-------------
edgar
18
riemann
28
-------------修改老师的信息后-------------
student1的teacher为： jack
student2的teacher为： jack

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。

 

三、深拷贝

（1）、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。

（2）、深拷贝实例

public class DeepCopy {
    public static void main(String[] args) throws CloneNotSupportedException {
        Teacher teacher = new Teacher();
        teacher.setName("riemann");
        teacher.setAge(28);

        Student student1 = new Student();
        student1.setName("edgar");
        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("jack");
        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-------------
edgar
18
riemann
28
-------------修改老师的信息后-------------
student1的teacher为： jack
student2的teacher为： riemann

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。

 

参考：

Java深入理解深拷贝和浅拷贝区别