【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();
             }
         }
     }
 }