1.什么是单例模型

2.懒汉模式

/**
 * 单例模型-懒汉模式
 * 
 * @author Administrator
 *
 */
public class Singleton {

	private static Singleton instance = null; // instance 一开始没有引用任何对象
	private final static ReentrantLock lock = new ReentrantLock();

	private Singleton() {

	}

	/**
	 * 调用getIntance()方法，才建立instance的引用对象
	 * 
	 * @return
	 */
	public static Singleton getIntance() {

		lock.lock();
		try {
			if (instance == null) {
				instance = new Singleton();
			}
		} finally {
			lock.unlock();
		}
		return instance;

	}

}

3.饿汉模式


/**
 * 单例：饿汉模式
 * @author Administrator
 *
 */
public class Singleton2 {
	
	private final static Singleton2 instance
	= new Singleton2();//JVM保证线程安全
	
	private Singleton2() {}
	
	
	public static Singleton2 getIntance() {
		return instance;
	}
}