shadow clone and deep clone

要让一个对象进行克隆，其实就是两个步骤： 

  1. 让该类实现java.lang.Cloneable接口； 
  2. 重写（override）Object类的clone()方法。

⑴浅复制（浅克隆）
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。换言之，浅复制仅仅复制所考虑的对象，而不

复制它所引用的对象。

⑵深复制（深克隆）
被复制对象的所有变量都含有与原来的对象相同的值，除去那些引用其他对象的变量。那些引用其他对象的变量将指向被复制过的新对象，而不再是原

有的那些被引用的对象。换言之，深复制把要复制的对象所引用的对象都复制了一遍。

Shadow Clone:

public class Professor implements Cloneable{
    
    public int ID;
    public String name;  
}

 

public class Student implements Cloneable{

    public int ID;
    public Professor mProfessor;
    
    public Student() {
        mProfessor = new Professor();
    }

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

    public static void main(String[] args) throws CloneNotSupportedException { 
        //deep clone: the reference of mProfessor is not changed
        Student s1 = new Student();
        s1.ID = 123;
        s1.mProfessor.name = "abc";
        Student s2 = (Student)s1.clone();
        System.out.println(s2.ID); //123
        System.out.println(s2.mProfessor.name); //abc

        s1.ID = 456;
        s1.mProfessor.name = "def";
        System.out.println(s2.ID);//123
        System.out.println(s2.mProfessor.name); //def
    }
}

result:

123
abc
123
def

Deep Clone:

public class Professor implements Cloneable{
    
    public int ID;
    public String name;

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

public class Student implements Cloneable{

    public int ID;
    public Professor mProfessor;
    
    public Student() {
        mProfessor = new Professor();
    }

    @Override
    protected Object clone() throws CloneNotSupportedException {
        Student student = (Student)super.clone();
        student.mProfessor = (Professor)student.mProfessor.clone();
        return student;
    }

    public static void main(String[] args) throws CloneNotSupportedException { 
        //deep clone: the reference of mProfessor is not changed
        Student s1 = new Student();
        s1.ID = 123;
        s1.mProfessor.name = "abc";
        Student s2 = (Student)s1.clone();
        System.out.println(s2.ID); //123
        System.out.println(s2.mProfessor.name); //abc

        s1.ID = 456;
        s1.mProfessor.name = "def";
        System.out.println(s2.ID);//123
        System.out.println(s2.mProfessor.name); //abc
    }
}

result:

123
abc
123
abc