trylock方法

synchronized 是不占用到手不罢休的，会一直试图占用下去。

与 synchronized 的钻牛角尖不一样，Lock接口还提供了一个trylock方法。
trylock会在指定时间范围内试图占用，占成功了，就啪啪啪。 如果时间到了，还占用不成功，扭头就走~

注意： 因为使用trylock有可能成功，有可能失败，所以后面unlock释放锁的时候，需要判断是否占用成功了，如果没占用成功也unlock,就会抛出异常

 

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package multiplethread;   import java.text.SimpleDateFormat; import java.util.Date; import java.util.concurrent.TimeUnit; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock;   public class TestThread {       public static String now() {         return new SimpleDateFormat("HH:mm:ss").format(new Date());     }       public static void log(String msg) {         System.out.printf("%s %s %s %n", now() , Thread.currentThread().getName() , msg);     }       public static void main(String[] args) {         final Lock lock = new ReentrantLock();           Thread t1 = new Thread() {             public void run() {                 boolean locked = false;                 try {                     log("线程启动");                     log("试图占有对象：lock");                       locked = lock.tryLock(1,TimeUnit.SECONDS);                     if(locked){                         log("占有对象：lock");                         log("进行5秒的业务操作");                         Thread.sleep(5000);                     }                     else{                         log("经过1秒钟的努力，还没有占有对象，放弃占有");                     }                   } catch (InterruptedException e) {                     e.printStackTrace();                 } finally {                                           if(locked){                         log("释放对象：lock");                         lock.unlock();                     }                 }                 log("线程结束");             }         };         t1.setName("t1");         t1.start();         try {             //先让t1飞2秒             Thread.sleep(2000);         } catch (InterruptedException e1) {             // TODO Auto-generated catch block             e1.printStackTrace();         }         Thread t2 = new Thread() {               public void run() {                 boolean locked = false;                 try {                     log("线程启动");                     log("试图占有对象：lock");                       locked = lock.tryLock(1,TimeUnit.SECONDS);                     if(locked){                         log("占有对象：lock");                         log("进行5秒的业务操作");                         Thread.sleep(5000);                     }                     else{                         log("经过1秒钟的努力，还没有占有对象，放弃占有");                     }                   } catch (InterruptedException e) {                     e.printStackTrace();                 } finally {                                           if(locked){                         log("释放对象：lock");                         lock.unlock();                     }                 }                 log("线程结束");             }         };         t2.setName("t2");         t2.start();     }   }