把flag改成一个Integer即可

/**
 * @author huangke
 * @date 2021/7/14 11:33
 *
 * 3个Condition队列交替打印
 */
public class JiaoTiShuziZimu4 {

    static volatile Integer count = 0;

    public static void main(String[] args) {
        ReentrantLock lock = new ReentrantLock();
        Condition conditionT1 = lock.newCondition();
        Condition conditionT2 = lock.newCondition();
        Condition conditionT3 = lock.newCondition();

        Thread t1 = new Thread(() -> {
            try {
                lock.lock();
                count++;
                for (int i = 1; i <= 26; i++) {
                    System.out.println('a');
                    // 叫醒t2
                    conditionT2.signal();
                    // 加入t1并wait()
                    conditionT1.await();
                }
                conditionT2.signal();
                System.out.println("队列1结束运行");
            }catch (Exception e){
                e.printStackTrace();
            }finally {
                lock.unlock();
            }
        });

        Thread t2 = new Thread(() -> {
            try {
                lock.lock();
                if (count != 1){
                    // 加入t2并wait()
                    conditionT2.await();
                }
                count++;
                for (int i = 1; i <= 26; i++) {
                    System.out.println((char)('b'));
                    // 叫醒t3
                    conditionT3.signal();
                    // 加入t2并wait()
                    conditionT2.await();
                }
                conditionT3.signal();
                System.out.println("队列2结束运行");
            }catch (Exception e){
                e.printStackTrace();
            }finally {
                lock.unlock();
            }
        });

        Thread t3 = new Thread(() -> {
            try {
                lock.lock();
                if (count != 2){
                    // 加入t3并wait()
                    conditionT3.await();
                }
                for (int i = 1; i <= 26; i++) {
                    System.out.println((char)('c'));
                    // 叫醒t1
                    conditionT1.signal();
                    // 加入t3并wait()
                    conditionT3.await();
                }
                conditionT1.signal();
                System.out.println("队列3结束运行");
            }catch (Exception e){
                e.printStackTrace();
            }finally {
                lock.unlock();
            }
        });

        t3.start();
        t2.start();
        t1.start();
    }

}