[实验任务一]：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。

1. 类图

1. 源代码

//StudentID.java

package test7;

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("20224083");

        } 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;

    }

}

//Client.java

package test7;

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));

    }

}

运行截图