后端面试每日一题启动 3 个线程，第一个线程打印 0，第二个打印 1，第三个打印 2...

布满荆棘的人生 2022-10-20 15:00 91阅读 0赞

启动 3 个线程，第一个线程打印 0，第二个打印 1，第三个打印 2，然后第一个线程打印 3，依次类推，直到打印指定的数字为止，例如 20；

public class DemoTask implements Runnable { 
    
        // 这里将lock对象换成 Lock(ReentrantLock) 进行lock/unlock也是可以的
        private static final Object lock = new Object();
        private static final int MAX = 30;
        private static int current = 1;
    
        private int index;
    
        public DemoTask(int index) { 
            this.index = index;
        }
    
        @Override
        public void run() { 
    
            synchronized (lock) { 
                // 退出条件
                while (current <= MAX) { 
                    // 到我执行了
                    if (current % 3 == index) { 
                        // current ++
                        System.out.println(Thread.currentThread().getName() + "------------" + current++);
                        // 释放锁
                        lock.notifyAll();
                    } else { 
                        System.out.println("NO" + Thread.currentThread().getName() + current);
                        try { 
                            lock.wait();
                        } catch (InterruptedException e) { 
                            e.printStackTrace();
                        }
                    }
                }
            }
        }
    
        public static void main(String[] args) throws Exception { 
            List<Thread> threadList = Arrays.asList(
                    new Thread(new DemoTask(0), "C"),
                    new Thread(new DemoTask(1), "A"),
                    new Thread(new DemoTask(2), "B")
            );
    
            threadList.forEach(Thread::start);
            for (Thread thread : threadList) { 
                thread.join();
            }
        }
    }