题解 | #多线程#

使用join函数

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main implements Runnable {
    public static String s = new String();
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        while (in.hasNextInt()) { // 注意 while 处理多个 case
            int n = in.nextInt();
            String[] s2 = {"A", "B", "C", "D"};
            Runnable runnable = new Main();
            for (int i = 0; i < n; i++) {
                for (int j = 0; j < s2.length; j++) {
                    Thread thread = new Thread(runnable);
                    s = s2[j];
                    thread.start();
                    try {
                        thread.join();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
            System.out.println();
        }
    }
    @Override
    public void run() {
        System.out.print(s);
    }
}