我只是想用两个线程来增加变量，但有时会显示值不正确。

public class SynchBlock {
public static void main(String[] args) throws InterruptedException {
        SynchBlock obj= new SynchBlock();
        obj.dowork();
}
    }

同步块法

private int count;
    public void call() {
        synchronized (this) {
            count++;
        }
    }

synchblock运行线程的方法

public void dowork() throws InterruptedException {
        th1.start();
        th2.start();
        th1.join();
        th1.join();
        System.out.println(count);
    }

线程类1只是增加了count的值

Thread th1 = new Thread(new Runnable() {

        public void run() {
            for (int i = 0; i < 10000; i++) {
                call();
            }
        }

    });

线程类2只是增加了count的值

Thread th2 = new Thread(new Runnable() {

        public void run() {
            for (int i = 0; i < 10000; i++) {
                call();
            }
        }

    });