java - 无法在多线程中实现同步

Question

我基本上是在尝试实现一个多人在线预订一辆出租车的现实生活示例。在我的代码中，我有 3 个类——出租车、客户和服务器。
必须有多个客户(线程)和一辆出租车。但我无法做到这一点。每次我创建新客户时，都会创建一个新的出租车实例。
这是出租车类别代码-

    public class taxi  {
        boolean BOOKED=false;
         String id;
        void book(){
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            BOOKED=true;
            System.out.println("Customer "+Thread.currentThread().getName()+" BOOKED taxi");
        }

        void release(){
            BOOKED=false;
            System.out.println("Customer "+Thread.currentThread().getName()+" RELEASED taxi");
        }

        void setId(String id){
            this.id=id;
        }

        String getId(){
            return id;
        }

    }

客户类别代码-

public class customer extends Thread {
     taxi t=new taxi();
        public  void run(){
            //System.out.println(t.hashCode());
            t.setId(Thread.currentThread().getName());
            System.out.println("Customer "+Thread.currentThread().getName()+" trying to BOOK taxi");
            t.book();
            System.out.println("Customer "+Thread.currentThread().getName()+" is currently USING taxi");

            try {


Thread.sleep(2000);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        System.out.println("Customer "+Thread.currentThread().getName()+" RELEASING taxi");
        t.release();
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        System.out.println("taxi used by customer "+Thread.currentThread().getName()+" set id to "+t.getId());
    }



}

服务器类代码-

public class server {

public static void main(String args[]){

         customer A=new customer();
         customer B=new customer();
         customer C=new customer();
         customer D=new customer();
        Thread t=new Thread();
         A.setName("A");
         B.setName("B");
         C.setName("C");
         D.setName("D");

         A.start();
         B.start();
         C.start();
         D.start();




    }


    }

这是我的输出-

Customer B trying to BOOK taxi
Customer D trying to BOOK taxi
Customer A trying to BOOK taxi
Customer C trying to BOOK taxi
Customer B BOOKED taxi
Customer A BOOKED taxi
Customer A is currently USING taxi
Customer D BOOKED taxi
Customer D is currently USING taxi
Customer B is currently USING taxi
Customer C BOOKED taxi
Customer C is currently USING taxi
Customer C RELEASING taxi
Customer C RELEASED taxi
Customer D RELEASING taxi
Customer D RELEASED taxi
Customer A RELEASING taxi
Customer A RELEASED taxi
Customer B RELEASING taxi
Customer B RELEASED taxi
taxi used by customer D set id to D
taxi used by customer C set id to C
taxi used by customer A set id to A
taxi used by customer B set id to B

正如您所看到的，每辆出租车的 ID 都是不同的，而不是相同。
请帮忙。

Answer 1

有关代码的一些要点:

1. 您应该仅创建 Taxi 类的单个实例，并从 Customer 类中删除taxi 实例变量，并在服务器类中实例化 Taxi。
2. 更改您的客户类别以乘坐共享出租车。您可以在 Customer 类中创建一个参数化构造函数来初始化共享出租车。
3. setId 应该在方法 book 中调用，这样出租车的 ID 只能由想要预订出租车的线程更改。

您可以在Taxi类中使用这种等待/通知机制来实现同步:

public class Taxi {
    Boolean BOOKED = false;
    String id;

    void book() throws InterruptedException {
        synchronized (this) {
            while (BOOKED) {
                this.wait();
            }
            try {
                setId(Thread.currentThread().getName());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            BOOKED = true;
            System.out.println("Customer " + Thread.currentThread().getName() + " BOOKED taxi");
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }

    void release() throws InterruptedException {
        synchronized (this) {
            BOOKED = false;
            System.out.println("Customer " + Thread.currentThread().getName() + " RELEASED taxi");
            this.notifyAll();
        }
    }

    void setId(String id) throws InterruptedException {
        System.out.println("SETTING ID TO CUSTOMER " + Thread.currentThread().getName());
        this.id = id;
    }

    String getId() {
        return id;
    }
}

客户:

   public class Customer extends Thread {
    Taxi taxi;

    public Customer(Taxi taxi){
        this.taxi = taxi;
    }

    public  void run(){
        //System.out.println(t.hashCode());

        System.out.println("Customer "+Thread.currentThread().getName()+" trying to BOOK taxi");
        try {
            taxi.book();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("Customer "+Thread.currentThread().getName()+" is currently USING taxi");

        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        System.out.println("Customer "+Thread.currentThread().getName()+" RELEASING taxi");
        try {
            taxi.release();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}