java设计模式单例模式

package Test;

public class ThreadAndSingleton {

	private ThreadAndSingleton() {
	}

	private static ThreadAndSingleton threadAndSingleton = null;

	/**
	 * 试试不加synchronized关键字，会出现两个实例的
	 * @param sleepTime
	 * @return
	 */
	public static synchronized ThreadAndSingleton getIntstance(int sleepTime) {
		if (threadAndSingleton == null) {
			try {
				Thread.sleep(sleepTime);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
			threadAndSingleton = new ThreadAndSingleton();
		}
		return threadAndSingleton;
		
	}

	public static void main(String[] args) {
		/**
		 * 下面这就属于模型驱动模式
		 */
		Thread th1 = new Thread(new Runnable() {
			@Override
			public void run() {
				System.out.println("th1:" + ThreadAndSingleton.getIntstance(1000));
			}
		});
		Thread th2 = new Thread(new Runnable() {
			@Override
			public void run() {
				System.out.println("th2:" + ThreadAndSingleton.getIntstance(0));
			}
		});
		th1.start();
		th2.start();
	}
}

　　关于

getIntstance方法被同步的说明：如果不同步，同事访问这个方法可能造成进入后等待，然后另一次访问开始了，结果造成两个实例，就不是单例模式了。