多线程 锁 synchronized 的使用

例子
1，synchronized锁住increase方法
2，volatile不能保证原子性 。这时需要用锁来保证,在increase方法加上synchronized

public class VolatileTest {

    public volatile int inc = 0;

    public synchronized  void increase() {
        inc++;
    }

    public static void main(String[] args) throws InterruptedException {
        final VolatileTest test = new VolatileTest();
        for (int i = 0; i < 10; i++) {
            new Thread(() -> {
                for (int j = 0; j < 1000; j++)
                    test.increase();
            }).start();
        }
        //保证前面的线程都执行完
        Thread.sleep(3000);
        System.out.println(test.inc);
    }

}