设计模式 单例模式

继续设计模式，这个模式用得应该非常频繁啊，并且也比較简单，假设如今你还不能纸笔随手写个单例出来，你就得加油了哈~

直接介绍几种线程安全的且我认为还比較不错的方式：

1、是不是号称恶汉，就是类载入就初始化了

package com.zhy.pattern.singlton;

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

package com.zhy.pattern.singlton;


public class Singleton02
{
	private static Singleton02 instance;

	public static Singleton02 getInstance()
	{
		if (instance == null)
		{
			synchronized (Singleton02.class)
			{
				if (instance == null)
				{
					instance = new Singleton02();
				}
			}
		}
		return instance;
	}
}

public enum Singleton03
{
	INSTANCE;
}

package com.zhy.pattern.singlton;

public class Singleton04
{
	private static final class InstanceHolder
	{
		private static Singleton04 INSTANCE = new Singleton04();
	}

	public static Singleton04 getInstance()
	{
		return InstanceHolder.INSTANCE;
	}
}