单例模式

饿汉式

class Singleton{

private static Singleton instance = new Singleton();

private Singleton(){//something}

public static  Singleton getInstance(){

return instance;

}

}

懒汉式

class Singleton{

private static Singleton instance = null;

pirvate Singleton(){//something}

public static Singleton getInstance(){

if(instance== null){

 instance= new Singleton();

}

return instance;

}

}