synchronized 同步对象概念

 

解决上述问题之前，先理解
synchronized关键字的意义
如下代码：

 

Object someObject =new Object();

synchronized (someObject){

//此处的代码只有占有了someObject后才可以执行

}

 

synchronized表示当前线程，独占 对象 someObject
当前线程独占 了对象someObject，如果有其他线程试图占有对象someObject，就会等待，直到当前线程释放对someObject的占用。
someObject 又叫同步对象，所有的对象，都可以作为同步对象
为了达到同步的效果，必须使用同一个同步对象

释放同步对象的方式： synchronized 块自然结束，或者有异常抛出

 

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package multiplethread;    import java.text.SimpleDateFormat; import java.util.Date;     public class TestThread {           public static String now(){         return new SimpleDateFormat("HH:mm:ss").format(new Date());     }           public static void main(String[] args) {         final Object someObject = new Object();                    Thread t1 = new Thread(){             public void run(){                 try {                     System.out.println( now()+" t1 线程已经运行");                     System.out.println( now()+this.getName()+ " 试图占有对象：someObject");                     synchronized (someObject) {                                                    System.out.println( now()+this.getName()+ " 占有对象：someObject");                         Thread.sleep(5000);                         System.out.println( now()+this.getName()+ " 释放对象：someObject");                     }                     System.out.println(now()+" t1 线程结束");                 } catch (InterruptedException e) {                     // TODO Auto-generated catch block                     e.printStackTrace();                 }             }         };         t1.setName(" t1");         t1.start();         Thread t2 = new Thread(){                public void run(){                 try {                     System.out.println( now()+" t2 线程已经运行");                     System.out.println( now()+this.getName()+ " 试图占有对象：someObject");                     synchronized (someObject) {                         System.out.println( now()+this.getName()+ " 占有对象：someObject");                         Thread.sleep(5000);                         System.out.println( now()+this.getName()+ " 释放对象：someObject");                     }                     System.out.println(now()+" t2 线程结束");                 } catch (InterruptedException e) {                     // TODO Auto-generated catch block                     e.printStackTrace();                 }             }         };         t2.setName(" t2");         t2.start();     }         }