單例模式的Java編程簡單實現

一、懶漢模式

具體如下：

/* Create a Singleton class */
class Singleton {
	public static Singleton getInstance(){
		return instance;
	}

	private static final Singleton instance = new Singleton();

	private Singleton(){ 
		System.out.println("Singleton()");
	}
}

public class Lazy{
	public static void main(String args[]){
		Singleton s1 = Singleton.getInstance();
		Singleton s2 = Singleton.getInstance();
		Singleton s3 = Singleton.getInstance();
	}
}

二、餓漢模式

方法1、使用同步方法，線程安全，效率低

/**
  *		getInstance() with synchronized
  */

class Singleton {

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

	private static Singleton instance = null;

	private Singleton(){
		System.out.println("Singleton()");
	}
}

public class Hungry {
	public static void main(String args[]){
		Singleton s1 = Singleton.getInstance();
		Singleton s2 = Singleton.getInstance();
		Singleton s3 = Singleton.getInstance();
	}
}

方法2、使用同步代碼塊，線程安全，效率高

/**
  *		getInstance() inner content with synchronized
  */

class Singleton {

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

	private static Singleton instance = null;

	private Singleton(){
		System.out.println("Singleton()");
	}
}

public class Hungry2 {
	public static void main(String args[]){
		Singleton s1 = Singleton.getInstance();
		Singleton s2 = Singleton.getInstance();
		Singleton s3 = Singleton.getInstance();
	}
}

方法3、靜態內部類，沒有性能損耗

/**
  *		inner static class with synchronized
  */

class Singleton {

	public static final Singleton getInstance(){
		return SingletonHolder.instance;
	}

	private Singleton(){
		System.out.println("Singleton()");
	}

	private static class SingletonHolder {
		private static final Singleton instance = new Singleton();
	}
}

public class Hungry3 {
	public static void main(String args[]){
		Singleton s1 = Singleton.getInstance();
		Singleton s2 = Singleton.getInstance();
		Singleton s3 = Singleton.getInstance();
	}
}

請參考該文章，有詳細講解，http://blog.csdn.net/jason0539/article/details/23297037/