单例模式

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

 

java

 

package rjsj.no7;

public class StudentID {
    private static StudentID instance = null;
    private String id;

    private StudentID(){}

    public static StudentID getInstance() {
        if (instance == null) {
            System.out.println("学生信息注册，分配学号！");
            instance = new StudentID();
            instance.setStudentID("20193288");
        } else {
            System.out.println("学生信息已经被注册，获取其已经存在的学号！");
        }
        return instance;
    }

    private void setStudentID(String id) {
        this.id = id;
    }

    public String getStudentID() {
        return this.id;
    }
}

 

package rjsj.no7;

public class Client {
    public static void main(String a[]) {
        StudentID stu1,stu2;
        String id1,id2;
        System.out.println("第一次生成学生");
        stu1 = StudentID.getInstance();

        System.out.println("第二次生成学生");
        stu2 = StudentID.getInstance();

        System.out.println("两学生学号是否一致：" + (stu1==stu2));

        id1 = stu1.getStudentID();
        id2 = stu1.getStudentID();
        System.out.println("第一次产生的学号：" + id1);
        System.out.println("第二次产生的学号：" + id2);
        System.out.println("内容是否相等：" + id1.equalsIgnoreCase(id2));
        System.out.println("是否是相同对象：" + (id1==id2));
    }
}

 

C++

 

#include <iostream>

using namespace std;

class S_num{
private:
    static S_num sno;
    static int num;
public:
    static S_num getintance() {
        // TODO Auto-generated method stub
        if(num==0) {
            cout<<"第一次办理学生证，分配新号码！"<<endl;
            sno.setNum(20193288);
        }
        else {
            cout<<"重复办理学生证，获取旧号码！"<<endl;
        }
        return sno;
    }
    int getNum() {
        return num;
    }
    void setNum(int n) {
        num = n;
    }
};

int S_num::num = 0;
S_num S_num::sno = S_num();

int main()
{
    S_num sno1=S_num().getintance();
    cout<<"第一次获取学号"<<sno1.getNum()<<endl;
    S_num sno2=S_num().getintance();
    cout<<"第二次获取学号"<<sno2.getNum()<<endl;
    cout<<"内容是否相等："<<(sno1.getNum()==sno2.getNum())<<endl;
    //cout<<"是否是相同对象："<<(sno1==sno2)<<endl;
}

 

 运行截图