java 线程 test

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import org.junit.Test;   public class testThread {       @Test     public  void testThreads() throws Exception {         Thread add = new AddThread();         Thread dec = new DecThread();         dec.start();         add.start();         add.join();         dec.join();           System.out.println(Counter.count+"ss");       } }   class Counter {     public static final Object lock = new Object();     public static int count = 0; }   class AddThread extends Thread {     public void run() {         for (int i=0; i<10000; i++) {                 synchronized (Counter.lock) {                     Counter.count += 1;                 }         }         System.out.println(Counter.count);     } }   class DecThread extends Thread {     public void run() {         for (int i=0; i<10000; i++) {             synchronized(Counter.lock) {                 Counter.count += 1;             }         }         System.out.println(Counter.count);     } }<br><br>

13063
20000
20000ss 

　得出结论，只有在synchronized内 线程变量才是安全的。