懒汉式单例,先写代码后边加解释
class Singleton{ private static Singleton instance ; private Singleton() { System.out.println("-->懒汉式单例模式开始调用构造函数"); } public static Singleton getInstance() { System.out.println("-->懒汉式单例模式开始调用公有方法返回实例"); if(instance == null) { instance = new Singleton(); }else{ System.out.println("-->懒汉式构造函数的实例已经被创建"); } System.out.println("-->方法调用结束,返回单例"); return instance; } public static void print() { System.out.println("hello world"); } } public class Test04 { public static void main(String[] args) { Singleton singleton = null; singleton = Singleton.getInstance(); Singleton.print(); } }