深拷贝与浅拷贝的含义与用例

Java中有 基本数据类型（元类型），和 类的实例对象 这个引用数据类型。而一般使用 『 = 』号做赋值操作的时候。对于基本数据类型，实际上是拷贝的它的值，但是对于对象而言，其实赋值的只是这个对象的引用，将原对象的引用传递过去，他们实际上还是指向的同一个对象。

浅拷贝：

只对类中基本数据类型进行了拷贝，而对引用数据类型只是进行了引用的传递，而没有真实的创建一个新的对象，则认为是浅拷贝。

package copy;
/**
 * @Author Snail
 * @Describe 浅拷贝
 * @CreateTime 2019/6/23
 */
public class ShallowCopy {
    public static void main(String[] args) throws CloneNotSupportedException {
        Student student1 = new Student();
        student1.setAge(29);
        student1.setTeacher(new Teacher());
        //利用clone（）方法创建一个新的对象，实现了一次浅拷贝
        Student student2= (Student) student1.clone();

        System.out.println("student1::"+student1);
        System.out.println("student2::"+student2);
        //其对象（teacher）的地址空间是一样的，是浅拷贝的特征
        System.out.println("student1.getTeacher()::"+student1.getTeacher());
        System.out.println("student2.getTeacher()::"+student2.getTeacher());
//        student1::copy.Student@66a29884
//        student2::copy.Student@4769b07b
//        student1.getTeacher()::copy.Teacher@cc34f4d
//        student2.getTeacher()::copy.Teacher@cc34f4d

    }
}



class Teacher {
    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 int age;
    private Teacher teacher;
    
    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
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }

}

深拷贝：

在对类中引用数据类型（类的实例对象）进行拷贝的时候，创建了一个新的对象，并且复制其内的成员变量，则认为是深拷贝

package copy;
/**
 * @Author Snail
 * @Describe 深拷贝
 * @CreateTime 2019/6/23
 */
public class DeepCopy {
    public static void main(String[] args) throws CloneNotSupportedException {
        Student student1 = new Student();
        student1.setAge(29);
        student1.setTeacher(new Teacher());
        Student student2= (Student) student1.clone();

        System.out.println("student1::"+student1);
        System.out.println("student2::"+student2);
        //深拷贝，其引用数据类型地址空间不一致
        System.out.println("student1.getTeacher()::"+student1.getTeacher());
        System.out.println("student2.getTeacher()::"+student2.getTeacher());
//        student1::copy.Student@66a29884
//        student2::copy.Student@4769b07b
//        student1.getTeacher()::copy.Teacher@cc34f4d
//        student2.getTeacher()::copy.Teacher@17a7cec2

    }
}

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;
    }

    @Override
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}

class Student implements Cloneable{

    private int age;
    private Teacher teacher;

    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
    protected Object clone() throws CloneNotSupportedException {
        //深拷贝
        Student student=(Student) super.clone();
        //拷贝引用数据类型
        student.teacher= (Teacher) this.teacher.clone();
        return student;
    }

}

总结：

浅拷贝和深拷贝是相对的，如果一个对象内部只有基本数据类型，那用 clone() 方法获取到的就是这个对象的深拷贝，而如果其内部还有引用数据类型，那用 clone() 方法就是一次浅拷贝的操作。