java-multithread

##

public class test01 {
    public static void main(String[] args) throws InterruptedException {
        class Counter {
            private int count = 0;

            public void incre() {
                count += 1;
            }

            public int getCount() {
                return count;
            }
        }

        final Counter counter = new Counter();
        class CountingThread extends Thread {
            public void run() {
                for (int i = 0; i < 200000; ++i) {
                    System.out.println("thread id:"+this.getId());
                    counter.incre();
                }
            }
        }

        Thread thread1 = new CountingThread();
        Thread thread2 = new CountingThread();

        thread2.start();
        thread1.start();
        thread1.join();
        thread2.join();

        System.out.println("counter: "+counter.getCount());
    }
}

counter: 399998

使用synchronized修饰方法

public synchronized void incre() {
    count += 1;
}

使用synchronized修饰”关键区域”

public void incre() {
    synchronized (this) {
        count += 1;
    }
}

synchronized不能继承——也就是说，假如一个方法在基础类中是“ 同步”的，那么在衍生类过载版本中，它不会自动进入“同步”状态。