public class ThreadSychronizedTest {

    public static volatile  int num = 0;

    public static void increase() {
        num++;
    }

    public static void main(String[] args) throws InterruptedException {

        Thread[] threads 
 
= new Thread[10];
        for (int i = 0; i < threads.length; i++) {
            threads[i]=new Thread(new Runnable() {
                public void run() {
                    for (int j = 0; j <1000 ; j++) {
                        increase();
                    }
                }
            });
            threads[i] .start();
        }
        
        
 
//等待所有執行緒執行完
        for (Thread t:threads) {
            t.join();
        }
        //執行結果<=10000
        System.out.println(num);//1000*10=10000？
    }


}

底層執行過程