JAVA中的鎖

在JAVA只有一種鎖，物件鎖。如果按照物件的型別細分，又分為例項物件鎖和Class物件
鎖。即我們常稱的，物件鎖與類鎖。

一把鑰匙開一把鎖

鎖的作用就是防止意外情況的發生，把門一鎖就是幹，幹完開鎖還鑰匙走人，下一個繼續

例項物件鎖

public class SyncInThread {
    static class SyncInClassInstance  implements Runnable {
        private Integer a = 0;
        @Override
        public void run() {
            _run
 
();
        }
        private synchronized void _run(){
            a += 1;
            System.out.println(Thread.currentThread().getName()+":a="+a);
        }
    }
    public static void main(String[] args) throws InterruptedException {
        SyncInClassInstance syncTest = new SyncInClassInstance
 
() ;
        Thread t1 = new Thread(syncTest) ;
        t1.start();
        Thread t2 = new Thread(syncTest) ;
        t2.start();

        Thread.sleep(1000);
    }
}

**效果:**無論執行緒誰先誰後，物件裡a變數方法是按照順序來的

Thread-1:a=1
Thread-0:a=2

Process finished with exit code 0

類鎖【Class物件鎖】

public class SyncInThread {
    static
 
 class SyncInClassInstance  implements Runnable {
        @Override
        public void run() {
            try {
                System.out.println(Thread.currentThread().getName()+"正在獲取SyncTest類鎖");
                _run();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        private synchronized void _run() throws InterruptedException {
            synchronized(SyncTest.class){
                System.out.println(Thread.currentThread().getName()+"已獲取SyncTest類鎖");
                Thread.sleep(5000);
                System.out.println(Thread.currentThread().getName()+"已釋放SyncTest類鎖");
            }
        }
    }
    public static void main(String[] args) throws InterruptedException {
        SyncInClassInstance syncTest = new SyncInClassInstance() ;
        Thread t1 = new Thread(syncTest) ;
        t1.start();
        SyncInClassInstance syncTest2 = new SyncInClassInstance() ;
        Thread t2 = new Thread(syncTest2) ;
        t2.start();

        Thread.sleep(1000);
    }
}

**效果：**本例以語句塊方式同步類物件，多個物件例項也要配對等鑰匙

Thread-0正在獲取SyncTest類鎖
Thread-1正在獲取SyncTest類鎖
Thread-1已獲取SyncTest類鎖
Thread-1已釋放SyncTest類鎖
Thread-0已獲取SyncTest類鎖
Thread-0已釋放SyncTest類鎖

Process finished with exit code 0