单例模式--Java实现

具体代码

//Main.java
package org.example.test006;

public class Main {
    public static void main(String[] args) {
        System.out.println("分配学号：");
        StudentNumber s1 =new StudentNumber();
        StudentNumber s2=new StudentNumber();

        s1=StudentNumber.getInstance(s1,1);
        s2=StudentNumber.getInstance(s2,2);

        String s11,s22;

        s11=s1.getStudentNumber();
        s22=s2.getStudentNumber();
        System.out.println("s1的学号为："+s11);
        System.out.println("s2的学号为："+s22);

        System.out.println("查看s1和s2是否为同一个学号:");
        System.out.println(s1==s2);

        System.out.println("尝试再次为s1分配学号：");
        s1=StudentNumber.getInstance(s1,3);

        System.out.println("查看s1和s2的学号是否相同:");
        System.out.println(s11==s22);

    }
}


//StudentNumber.java
package org.example.test006;

public class StudentNumber {
    public String getStudentNumber() {
        return studentNumber;
    }

    public void setStudentNumber(String studentNumber) {
        this.studentNumber = studentNumber;
    }

    private String studentNumber;

    StudentNumber(){}

    public static StudentNumber instance=null;

    public static StudentNumber getInstance(StudentNumber sn,int i){
        if(sn.getStudentNumber()==null){
            System.out.println("第"+i+"位学生还没有学号，分配新的学号：");
            instance=new StudentNumber();

            instance.setStudentNumber("20214063"+i);
        }else{
            System.out.println("已经有学号啦~");
        }

        return instance;
    }
}