Java克隆浅拷贝深拷贝拷贝构造器嵌套对象

Question

我编写了一个测试应用程序，以演示使用 Shallow、Deep 和 Copy 构造函数的 Java 克隆。

我使用 Shallow 和 Deep 实现了，但使用 Copy 构造函数我想我错过了一些东西。

请查看下面的代码并告诉我复制构造函数实现的修复方法。

public class CopyConstructorDemo {

    public static void main(String[] args) {

        Teacher teacher = new Teacher("Kripalu");
        Student sOrg = new Student(15007, "Amit", "Chirimiri", teacher);

        //Student sClo = sOrg;                          //Java Reference

        //Student sClo = (Student) sOrg.clone();        //CLONE


        Student sClo = new Student(sOrg);               //COPY CONSTRUCTOR

        sOrg.display();

        sClo.getTeacher().setName("ShriKrishn");

        sOrg.display();

    }


}

class Teacher implements Cloneable{

    String _name = "";

    Teacher(String name){
        this.setName(name);
    }

    String getName(){return _name;}
    void setName(String name){_name = name;}

    //For Deep copy
    //@Override
    protected Object clone(){

        try {
            return super.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
            return null;
        }

    }   
}

class Student implements Cloneable{

    int _rollNo;
    String _name;
    String _address;

    Teacher _teacher;

    Student(int rollNo, String name, String address, Teacher teacher){
        this.setRollNo(rollNo);
        this.setName(name);
        this.setAddress(address);

        _teacher = teacher;
    }

    Student(Student copyCons){
        this._rollNo = copyCons._rollNo;
        this._name = copyCons._name;
        this._address = copyCons._address;
        this._teacher = copyCons._teacher;

    }

    Teacher getTeacher(){return _teacher;}
    void setTeacher(Teacher teacher){_teacher = teacher;}

    int getRollNo(){return _rollNo;}
    String getName(){return _name;}
    String getAddress(){return _address;}

    void setRollNo(int rollNo){_rollNo = rollNo;}
    void setName(String name){_name = name;}
    void setAddress(String address){_address = address;}

    void display(){
        System.out.println(_rollNo+" "+
                           _name+" "+
                           _address+" "+
                           _teacher.getName());
    }

    @Override
    protected Object clone(){

        try {

            //return super.clone();     //For Shallow copy

            //For Deep copy
            Student cloned = (Student)super.clone();
            cloned.setTeacher((Teacher)cloned.getTeacher().clone());
            return cloned;

        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
            return null;
        }

    }



}

输出（复制构造函数）

15007 阿米特·奇里米里·克里帕卢

15007 Amit Chirimiri ShriKrishn

编辑：

由于学生类包含嵌套类（教师）引用，简单的复制构造函数将不起作用。我们必须对 Teacher 和 Student 类的 Copy 构造函数一起使用克隆（浅拷贝），这里更改了拷贝构造函数

Student(Student copyCons){

    this._rollNo = copyCons._rollNo;
    this._name = copyCons._name;
    this._address = copyCons._address;
    this._teacher = (Teacher) copyCons._teacher.clone();  //FIX: thanks to Amir

}

其余代码相同。

Answer 1

复制构造函数和克隆方法应该是这样的：

对于学生：

 //Copy constructor for the student
 Student(Student copyCons){
    this._rollNo = copyCons._rollNo;
    this._name = copyCons._name;
    this._address = copyCons._address;
    this._teacher = copyCons._teacher.clone();
}

 //Clone for the student
 protected Student clone(){
     return new Student(this);
 }

对于老师：

//This is the copy constructor
Teacher(Teacher t){
        setName(t.getName());
 }

//That's how you clone an object of type teacher
protected Teacher clone(){
   return new Teacher(this);
}

使用示例：

Teacher t1 =  new teacher("Teacher 1");
Teacher t1Clone = t1.clone();

Student s1 = new Student(15007, "Amit", "Chirimiri", t1);
Student s1Clone = s1.clone();