単例模式（设计模式）

饿汉式

public class Singleton{
	private Singleton(){};
	private static Singleton instance = new Singleton();
	public static Singleton getInstance(){
		return instance;
	}
}

懒汉式

public class Singleton{
private static Singleton instance = null;
	public static synchronized Singleton getInstance(){;
		if(instance == null){
			instance = new Singleton();
			return instance;
		}
	}
}