JAVA单例模式示例

package com.eboy.single;

public class singleDemo {
    
    public static void main(String[] args){
        Single s1 = Single.getInstance();
        Single s2 = Single.getInstance();
        
        System.out.println(s1 == s2); //true
        
        Single2 s3 = Single2.getInstance();
        Single2 s4 = Single2.getInstance();
        System.out.println(s3 == s4); //true
        
    }

}

//以下是懒汉模式(延迟加载模式)，类加载进来，没有对象，只有调用了getInstance方法时，才会创建对象，而且是线程安全的
class Single2{
    private static Single2 s = null;
    
    private Single2(){
        
    }
    
    public static Single2 getInstance(){
        if (s == null){
            synchronized (Single2.class) {
                if (s ==null){
                    s = new Single2();
                }
            }            
        }
        return s;
    }
}