package com.company.calcul; import java.util.concurrent.locks.Condition; import java.util.concurrent.locks.ReentrantLock; public class Thread1 { public static void main(String[] args) { ReentrantLock reentrantLock = new ReentrantLock(); Condition condition1 = reentrantLock.newCondition(); Condition condition2 = reentrantLock.newCondition(); Condition condition3 = reentrantLock.newCondition(); Thread threadA = new Thread(() -> { reentrantLock.lock(); try { condition1.await(); System.out.println("A"); condition2.signal(); } catch (InterruptedException e) { e.printStackTrace(); } finally { reentrantLock.unlock(); } }); Thread threadB = new Thread(() -> { reentrantLock.lock(); try { condition2.await(); System.out.println("B"); condition3.signal(); } catch (InterruptedException e) { e.printStackTrace(); } finally { reentrantLock.unlock(); } }); Thread threadC = new Thread(() -> { reentrantLock.lock(); try { condition3.await(); System.out.println("C"); } catch (InterruptedException e) { e.printStackTrace(); } finally { reentrantLock.unlock(); } }); reentrantLock.lock(); try { threadA.start(); threadB.start(); threadC.start(); condition1.signal(); } finally { reentrantLock.unlock(); } } } 这个为什么没有输出ABC

这段代码没有输出ABC是因为在调用condition1.signal()之前，主线程已经释放了锁。

在代码中，主线程先获取了锁reentrantLock.lock()，然后启动了线程A、B、C，并调用condition1.signal()来唤醒线程A。但是，在调用signal()方法之前，主线程调用了reentrantLock.unlock()释放了锁。

由于线程A、B、C在启动后会尝试获取锁并进入等待状态，而此时主线程已经释放了锁，线程A无法获取到锁并继续执行，所以最终没有输出ABC。

为了修正这个问题，可以将reentrantLock.lock()方法的调用位置移动到condition1.signal()之前，确保在调用signal()方法之前保持锁的持有状态。

修正后的代码如下：

package com.company.calcul;

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;

public class Thread1 {
    public static void main(String[] args) {

        ReentrantLock reentrantLock = new ReentrantLock();
        Condition condition1 = reentrantLock.newCondition();
        Condition condition2 = reentrantLock.newCondition();
        Condition condition3 = reentrantLock.newCondition();

        Thread threadA = new Thread(() -> {
            reentrantLock.lock();
            try {
                condition1.await();
                System.out.println("A");
                condition2.signal();
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                reentrantLock.unlock();
            }
        });

        Thread threadB = new Thread(() -> {
            reentrantLock.lock();
            try {
                condition2.await();
                System.out.println("B");
                condition3.signal();
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                reentrantLock.unlock();
            }
        });

        Thread threadC = new Thread(() -> {
            reentrantLock.lock();
            try {
                condition3.await();
                System.out.println("C");
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                reentrantLock.unlock();
            }
        });

        reentrantLock.lock();
        try {
            threadA.start();
            threadB.start();
            threadC.start();
            condition1.signal();
        } finally {
            reentrantLock.unlock();
        }
    }
}

在修正后的代码中，主线程在启动子线程之前获取锁reentrantLock.lock()，然后启动子线程并调用condition1.signal()方法唤醒线程A，最后在finally块中释放锁reentrantLock.unlock()。这样可以确保线程A在调用signal()方法之前已经获取到了锁，并且其他线程也能正确执行并输出ABC。