Java Singleton（单例模式）

1.静态类内部加载

/**
 * Created by BlueMond on 2018/3/25.
 */
public class SingletonModel {
    private static class SingletonIn{
        public  static SingletonModel special = new SingletonModel();
    }
    private SingletonModel(){

    }
    public static SingletonModel instance(){ //static very important for the method be found, the SM() is private!!!
        return SingletonIn.special;
    }
}

2.双重校验锁法

public class SingletonDemo {
    private volatile static SingletonDemo instance;
    private SingletonDemo(){
        System.out.println("Singleton has loaded");
    }
    public static SingletonDemo getInstance(){
        if(instance==null){
            synchronized (SingletonDemo.class){
                if(instance==null){
                    instance=new SingletonDemo();
                }
            }
        }
        return instance;
    }
}