Lock

Lock

一、

1.

public class ThreadSynchronizedDemo {

	public static String name = "zhang" ;
	public static Integer age = 25 ;

	/**
	 * @param args
	 */
	public static void main(String[] args) {

		/**
		 * 预期输出:
		 * zhang : 25 
		 * li    : 24
		 * 实际输出:
		 * 各种组合，
		 * 原因：
		 * 线程的执行时无序的，谁先执行取决于谁先占用CPU
		 * 即，可能出现   先printDemo 打印一般的时候，ChangeDemo 生效修改了 其他的值
		 */
		new Thread(new PrintDemo()).start();
		new Thread(new ChangeDemo()).start();
	}

}

class PrintDemo implements Runnable{

	@Override
	public void run() {
		while(true){
			System.out.println("name:"+ThreadSynchronizedDemo.name+" age:"+ThreadSynchronizedDemo.age);
		}
	}

}

class ChangeDemo implements Runnable{

	@Override
	public void run() {
		while(true){
			if("zhang".equals(ThreadSynchronizedDemo.name)){
				ThreadSynchronizedDemo.name = "li";
				ThreadSynchronizedDemo.age = 24 ;
			}else{
				ThreadSynchronizedDemo.name = "zhang" ;
				ThreadSynchronizedDemo.age = 25 ;
			}
		}
	}

}

2.

public class ThreadSynchronizedDemo {

	public static String name = "zhang" ;
	public static Integer age = 25 ;

	public static void main(String[] args) {

		/**
		 * Synchronized:
		 * 代码块锁机制
		 * 1.锁加在哪：欲同步的位置
		 * 2.锁对象：
		 * 共享的资源/类的字节码 class / 某一不变的对象 private static final Object object
		 */
		new Thread(new PrintDemo()).start();
		new Thread(new ChangeDemo()).start();
	}

}

class PrintDemo implements Runnable{

	@Override
	public void run() {
		while(true){
			synchronized (ThreadSynchronizedDemo.class) {
				System.out.println("name:"+ThreadSynchronizedDemo.name+" age:"+ThreadSynchronizedDemo.age);
			}
		}
	}

}

class ChangeDemo implements Runnable{

	@Override
	public void run() {
		synchronized (ThreadSynchronizedDemo.class) {
			while(true){
				if("zhang".equals(ThreadSynchronizedDemo.name)){
					ThreadSynchronizedDemo.name = "li";
					ThreadSynchronizedDemo.age = 24 ;
				}else{
					ThreadSynchronizedDemo.name = "zhang" ;
					ThreadSynchronizedDemo.age = 25 ;
				}
			}
		}
	}

}