1.设计4个线程，其中两个线程每次对j增加1，另外两个线程对j每次减少1。 要求：使用内部类实现线程，对j增减的时候不考虑顺序问题。

public class Main {
    private int j = 0;

    public static void main(String[] args) {
        Main main = new Main();
        main.execute();
    }

    public void execute() {
        IncreaseThread increaseThread1 = new IncreaseThread();
        IncreaseThread increaseThread2 = new IncreaseThread();
        DecreaseThread decreaseThread1 = new DecreaseThread();
        DecreaseThread decreaseThread2 = new DecreaseThread();

        increaseThread1.start();
        increaseThread2.start();
        decreaseThread1.start();
        decreaseThread2.start();
    }

    class IncreaseThread extends Thread {
        @Override
        public void run() {
            for (int i = 0; i < 10; i++) {
                j++;
                System.out.println(Thread.currentThread().getName() + "增加了1，当前j的值为：" + j);
            }
        }
    }

    class DecreaseThread extends Thread {
        @Override
        public void run() {
            for (int i = 0; i < 10; i++) {
                j--;
                System.out.println(Thread.currentThread().getName() + "减少了1，当前j的值为：" + j);
            }
        }
    }
}