学号的单一

仿照课堂的身份证的例子，实现每个同学仅有一个学号这一问题。

类图

代码

2.1    StudentID.java
package danli;

public class StudentID {

    private static StudentID instance=null;
    private String ID; 

    public String getID() 
    {
        return ID;
    }     

    public void setID(String iD) 
    {
        ID = iD;
    } 

    private StudentID()
    {
        
    }     

    public static StudentID getStudentID()
    {

        if(instance==null) {
            instance=new StudentID();
            instance.setID("20204044");
        }
        else
        {
            System.out.println("一个学生只能有一个学号");
        }

        return instance;

    }
    
}

2.2    Client.java
package danli;

public class Client {

    public static void main(String[] args) {

        StudentID stu1,stu2;

        stu1=StudentID.getStudentID();

        stu2=StudentID.getStudentID();

        String str1,str2;

        str1=stu1.getID();

        str2=stu2.getID();

        System.out.println("第一次学号："+str1);

        System.out.println("第二次学号："+str2);

        }
    
}

#include<iostream>
using namespace std; 

class Student
{

private:
 string ID;
 static Student* instance ;
 Student(){} 

public:
string getID() {
return ID;
}

void setID(string iD) {
ID = iD;
}

static Student* getInstance(){
if (instance==NULL){
instance = new Student();
cout << "入学分配学号" << endl;
instance->setID("20204044");
}
else
cout << "已经入学，学号唯一" << endl;
return instance;
}

};

Student* Student::instance=NULL;

int _tmain(int argc, _TCHAR* argv[])
{
Student* s, *s1;
string sID, s1ID;
 
s = Student::getInstance();
s1 = Student::getInstance();

cout << "s的学号为" << s->getID() << endl;
cout << "s1的学号为" << s1->getID() << endl;
cout << "s的地址为" << s << endl;
cout << "s1的地址为" << s1 << endl;

system("pause");

return 0;

}