Java线程启动后未运行 桥梁车辆死锁模拟程序无输出问题排查

你当前的代码不需要拆分文件，全量代码只包含一个public类Cars，只要将文件命名为Cars.java即可正常编译运行，单文件完全满足需求，无需做拆分操作。

没有输出的核心原因是你继承Thread类后，没有重写类的run()方法：

• Thread类调用start()启动后，默认只会执行内部的run()方法，你将所有业务逻辑都放在了自定义的go()方法中，线程启动后go()从未被调用，因此没有任何内容输出。
• 另外代码里还有一处隐性bug：西向车辆的打印逻辑里，你误把字符串拼接的+写成了赋值符=，会导致name变量被意外覆盖：System.out.println(name = " are attempting to cross.");

1. 给ExtendThread类添加重写的run()方法，在内部调用你已经写好的go()方法，或者直接将go()方法改名为run()并添加@Override注解即可
2. 修正西向车辆打印逻辑的赋值bug，将=改为+

修正后的完整代码如下：

import java.util.concurrent.*;
public class Cars {
    // 静态内部类实现线程逻辑
    static class ExtendThread extends Thread {
        Semaphore sem;
        String name;

        public ExtendThread(Semaphore sem, String name) {
            super(name);
            this.sem = sem;
            this.name = name;
        }

        // 重写Thread的run方法
        @Override
        public void run() {
            go();
        }

        // 业务模拟逻辑
        public void go() {
            // 西向车辆逻辑
            if (this.getName().equals("Westbound Cars")) {
                try {
                    System.out.println(name + " are waiting to cross.");
                    sem.acquire();
                    // 修正了原来的赋值bug
                    System.out.println(name + " are attempting to cross.");
                    for (int i = 1; i < 9; i++) {
                        System.out.println("Westbound car " + i + " is waiting to cross.");
                        Thread.sleep(1000);
                        System.out.println("Westbound car " + i + " has crossed.");
                        Thread.sleep(1000);
                    }
                }
                catch (InterruptedException exc) {
                    System.out.println(exc);
                }
                System.out.println(name + " have crossed the bridge.");
                sem.release();
            }
            // 东向车辆逻辑
            else {
                System.out.println(name + " are waiting to cross the bridge.");
                try {
                    System.out.println(name + " is waiting to cross.");
                    sem.acquire();
                    System.out.println(name + " is attempting to cross.");
                    for (int i = 1; i < 9; i++) {
                        System.out.println("Eastbound car " + i + " is waiting to cross.");
                        Thread.sleep(1000);
                        System.out.println("Eastbound car " + i + " has crossed.");
                        Thread.sleep(1000);
                    }
                }
                catch (InterruptedException exc) {
                    System.out.println(exc);
                }
                System.out.println(name + " have crossed the bridge.");
                sem.release();
            }
        }
    }
    public static void main(String [] args) throws InterruptedException {
        Semaphore sem = new Semaphore(1);
        ExtendThread exTh1 = new ExtendThread(sem,"Westbound Cars");
        ExtendThread exTh2 = new ExtendThread(sem,"Eastbound Cars");
        exTh1.start();
        exTh2.start();
        exTh1.join();
        exTh2.join();
    }
}

内容的提问来源于stack exchange，提问作者Samantha Baughman