单例模式

package com.wdf;

public class Singleton {

	private volatile static Singleton singleton = null;

	private Singleton() {

	}

	public static Singleton getInstance() {

		if (singleton == null) {
			synchronized (Singleton.class) {
				//double checked locking
				if (singleton == null) {
					singleton = new Singleton();
				}
			}

		}

		return singleton;

	}
}