java - Java多线程如何让线程等待一段时间

Question

Parking Problem

There's n parking lots. On one parking lot, there can be only one car at a time. If all parking lots are occupied then the car will wait some time and if there's still no free parking lot then it leaves.

需要使用线程来解决(通过意志同步)。

这是我的代码:

parking

class Parking implements Runnable {
private Thread thread;
private String threadName;
static int parkingLots;

static {
    parkingLots = 5;
}

Parking(String threadName) {
    this.threadName = threadName;
}

public void run() {
    if (parkingLots > 0) {
        long restTime = (long) (Math.random() * 2000);
        try {
            parkingLots--;
            System.out.println("Car " + threadName + " stands in the parking lot");
            Thread.sleep(restTime);
        } catch (InterruptedException e) {
        }
        parkingLots++;
        System.out.println("Car " + threadName + " has left parking, it stood there" + ((double)restTime / (double)1000) + " s");
    } else
        System.out.println("Car " + threadName + " has left parking");
}

public void start() {
    if (thread == null) {
        thread = new Thread(this, threadName);
        thread.start();
    }
}
}

主要

public class Main {
    public static void main(String[] args) {
        ArrayList<Parking> parking = new ArrayList<Parking>();

        for (int i = 0; i < 15; i++) {
            parking.add(new Parking(String.valueOf(i + 1)));
        }
        for (Parking i: parking) {
            i.start();
        }
    }
}

我想看到什么(当有2个 parking 场和4辆车时):

Car 1 stands in the parking lot
Car 2 stands in the parking lot
Car 3 is waiting
Car 4 is waiting
Car 3 has left parking
Car 2 has left parking, it stood there 1.08 s
Car 4 stands in the parking lot
Car 1 has left parking, it stood there 1.71 s
Car 4 has left parking, it stood there 0.83 s

但是我得到的结果(当有 2 个 parking 场和 4 辆车时):所有第一辆车(1 和 2)都停在 parking 场，其他车(3 和 4)就离开了，因为没有免费 parking 场。即使有大约 15 辆车，他们仍然无法进入那里。

那么我怎样才能让汽车在出发前等待一段时间呢？如果有免费 parking 场，他们就会去 parking ，否则他们就会离开 parking 场。

Answer 1

修改了您的代码，看看是否有效。

public class Parking implements Runnable {
    private Thread thread;
    private String threadName;
    static int parkingLots;

    static {
        parkingLots = 5;
    }

    Parking(String threadName) {
        this.threadName = threadName;
    }

    public void run() {
        long restTime = (long) (Math.random() * 2000);
        if (parkingLots > 0) {
            checkparking();
        } else {
            try {
                System.out.println("Car " + threadName + " is waiting");
                Thread.sleep(restTime);
                System.out.println("Car " + threadName + " is checking for free parkinglot");
                checkparking();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }

    }

    public void checkparking() {
        if (parkingLots > 0) {
        long restTime = (long) (Math.random() * 2000);
        try {
            parkingLots--;
            System.out.println("Car " + threadName + " stands in the parking lot");
            Thread.sleep(restTime);
        } catch (InterruptedException e) {
        }
        parkingLots++;
        System.out.println(
                "Car " + threadName + " has left parking, it stood there" + ((double) restTime / (double) 1000) + " s");

    } else {
        System.out.println(
                "Car " + threadName + " has left since there is no parking space");
    }
    }

    public void start() {
        if (thread == null) {
            thread = new Thread(this, threadName);
            thread.start();
        }
    }

}

公共(public)类主要{

     public static void main(String[] args) {
            ArrayList<Parking> parking = new ArrayList<Parking>();

            for (int i = 0; i < 15; i++) {
                parking.add(new Parking(String.valueOf(i + 1)));
            }
            for (Parking i: parking) {
                i.start();
            }
        }
}

输出:

Car 2 stands in the parking lot
Car 1 stands in the parking lot
Car 7 is waiting
Car 5 stands in the parking lot
Car 3 stands in the parking lot
Car 6 is waiting
Car 4 stands in the parking lot
Car 9 is waiting
Car 8 is waiting
Car 10 is waiting
Car 11 is waiting
Car 12 is waiting
Car 13 is waiting
Car 14 is waiting
Car 15 is waiting
Car 4 has left parking, it stood there0.049 s
Car 14 is checking for free parkinglot
Car 14 stands in the parking lot
Car 5 has left parking, it stood there0.366 s
Car 2 has left parking, it stood there0.461 s
Car 12 is checking for free parkinglot
Car 12 stands in the parking lot
Car 15 is checking for free parkinglot
Car 15 stands in the parking lot
Car 1 has left parking, it stood there0.882 s
Car 9 is checking for free parkinglot
Car 9 stands in the parking lot
Car 10 is checking for free parkinglot
Car 10 has left since there is no parking space
Car 3 has left parking, it stood there1.014 s
Car 13 is checking for free parkinglot
Car 13 stands in the parking lot
Car 15 has left parking, it stood there0.937 s
Car 6 is checking for free parkinglot
Car 6 stands in the parking lot
Car 11 is checking for free parkinglot
Car 11 has left since there is no parking space
Car 13 has left parking, it stood there0.344 s
Car 7 is checking for free parkinglot
Car 7 stands in the parking lot
Car 8 is checking for free parkinglot
Car 8 has left since there is no parking space
Car 7 has left parking, it stood there0.054 s
Car 14 has left parking, it stood there1.731 s
Car 9 has left parking, it stood there1.359 s
Car 12 has left parking, it stood there1.877 s
Car 6 has left parking, it stood there1.787 s