4个线程操作一个变量，2个线程执行 1操作，2个线程执行-1操作

public class Test {
    public static int A = 0;
    public static Object object = new Object();
    public static void main(String[] args) throws InterruptedException {
        Thread thread1 = new Thread(new RunnableA());
        Thread thread2 = new Thread(new RunnableA());
        Thread thread3 = new Thread(new RunnableB());
        Thread thread4 = new Thread(new RunnableB());
        thread1.start();
        thread2.start();
        thread3.start();
        thread4.start();
    }
}
class RunnableA implements Runnable {
    @Override
    public void run() {
        synchronized (Test.object) {
            Test.A++;
        }
    }
}
class RunnableB implements Runnable {
    @Override
    public void run() {
        synchronized (Test.object) {
            Test.A--;
        }
    }
}

public class Test {
    public static void main(String[] args) throws InterruptedException {
        Data data = new Data();
        Thread thread1 = new Thread(new RunnableA(data));
        Thread thread2 = new Thread(new RunnableA(data));
        Thread thread3 = new Thread(new RunnableB(data));
        Thread thread4 = new Thread(new RunnableB(data));
        thread1.start();
        thread2.start();
        thread3.start();
        thread4.start();
    }
}
class Data {
    private int A = 0;
    public synchronized void increase() {
        A++;
    }
    public synchronized void decrease() {
        A--;
    }
    public int getA() {
        return A;
    }
}
class RunnableA implements Runnable {
    private Data data;
    public RunnableA(Data data) {
        this.data = data;
    }
    @Override
    public void run() {
        data.increase();
    }
}
class RunnableB implements Runnable {
    private Data data;
    public RunnableB(Data data) {
        this.data = data;
    }
    @Override
    public void run() {
        data.decrease();
    }
}