设计模式之三：单例模式（饿汉式与懒汉式）

//保证类在内存中只有一个对象

package com.xjh.demo.designpattern.pattern3;

public class Student {

    private Student(){

    }

    //懒汉式
    private static Student s=null;

    //懒汉式易出现线程安全问题：多线程环境、数据共享、多条语句操作数据
    public synchronized static Student getStudent(){
        if(s==null){
            s=new Student();
        }
        return s;
    }

   //饿汉式
    private static Student s=new Student();
    public static Student getStudent(){
        return s;
    }
}

package com.xjh.demo.designpattern.pattern3;

public class StudentTest {

    public static void main(String[] args) {
        Student s1 = Student.getStudent();
        Student s2 = Student.getStudent();
        System.out.println(s1 == s2);
    }
}