Java 浅拷贝与深拷贝的区别

浅拷贝

什么是浅拷贝

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。

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();
        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;
    }

}

输出结果：

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。

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。

深拷贝实例

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();
        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。

teacher姓名Delacey更改前:

teacher姓名Jam更改后:

参考资源

【Java深入】深拷贝与浅拷贝详解