《软件设计》-单例模式

[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。

类图

Java

StudentNp

package com.gazikel;

public class StudentNo {
    private static volatile StudentNo instance = null;
    private String no;
    private StudentNo(){

    }

    public static StudentNo getInstance(){
        if (instance == null) {
            synchronized (StudentNo.class) {
                if (instance == null) {
                    System.out.println("第一次创建学号，分配新号码");
                    instance = new StudentNo();
                    instance.setStudentNo("123");
                }
            }

        } else {
            System.out.println("重复创建学号，获取旧号码");
        }
        return instance;
    }

    private void setStudentNo(String no) {
        this.no = no;
    }

    public String getStudentNo() {
        return this.no;
    }
}

Client

package com.gazikel;

public class Client {

    public static void main(String[] args) {
        StudentNo no1, no2;
        no1 = StudentNo.getInstance();
        no2 = StudentNo.getInstance();

        if (no1 == no2) {
            System.out.println("该同学学号唯一");
        } else {
            System.out.println("该同学学号不唯一");
        }
        // System.out.println("学号是否一致" + (no1 == no2));

        System.out.println("------------------");
        String str1, str2;
        str1 = no1.getStudentNo();
        str2 = no2.getStudentNo();
        System.out.println("第一次号码：" + str1);
        System.out.println("第而次号码：" + str2);
        System.out.println("内容是否相等：" + str1.equalsIgnoreCase(str2));
        System.out.println("是否相同对象：" + (str1 == str2));
    }
}