【快手初面】要求3个线程按顺序循环执行，如循环打印A，B，C

【背景】这个题目是当时远程面试时，手写的题目。自己比较惭愧，当时写的并不好，面试完就又好好的完善了下。

一、题意分析

3个线程要按顺序执行，就要通过线程通信去控制这3个线程的执行顺序。

而线程通信的方式就有wait/notify, condition#await, condition#signal等

二、具体代码

public class Main {

    private static String lastCompleteStr = "C";

    public static void main(String[] args) {
        new Thread(new PrintTask("A", "C")).start();
        new Thread(new PrintTask("B", "A")).start();
        new Thread(new PrintTask("C", "B")).start();
    }

    static class PrintTask implements Runnable {

        private String cur;

        private String waitLastStr;

        public PrintTask(String cur, String waitLastStr) {
            this.cur = cur;
            this.waitLastStr = waitLastStr;
        }

        @Override
        public void run() {
            try {
                while (true) {
                    synchronized (Main.class) {
                        while (!lastCompleteStr.equals(waitLastStr)) {
                            Main.class.wait();
                        }

                        System.out.println(cur);

                        lastCompleteStr = cur;

                        Main.class.notifyAll();
                    }
                }
            } catch (Exception e ) {
                e.printStackTrace();
            }
        }
    }
}