生產者和消費者的Java同步隊列線程

Question

Java生產者 - 消費者程序使用線程&同步隊列，程序被分成3個類但它不能運行。

Queue.java：

public class Queue { 
    static final int MAXQUEUE = 3; 
    int[] queue = new int[MAXQUEUE]; 
    int front, rear; 
    public Queue(){ front = 0; rear = 0; } 
    public boolean isEmpty(){ return (front==rear); } 

    public boolean isFull(){ 
     int index = rear+1 < MAXQUEUE ? rear+1 : 0; 
     return (index == front); 
    } 

    public void enqueue(int value) { 
     queue[rear] = value; 
     rear = rear+1 < MAXQUEUE ? rear+1 : 0; 
    } 

    public int dequeue(){ 
     int data = queue[front]; 
     front = front+1 < MAXQUEUE ? rear+1 : 0; 
     return data; 
    } 
} 

SynchronizedQueue.java：

import java.util.Queue; 

public class SynchronizedQueue { 
    Queue queue; 
    public SynchronizedQueue() {queue = new Queue(); } 
    public synchronized void enqueue(int value) { 
     try { 
      while (queue.isFull()) { 
       System.out.println(); 
       System.out.println("Queue is full, please wait...."); 
       wait(); 
      } 
     } 
     catch (InterruptedException e) { } 
     ((SynchronizedQueue) queue).enqueue(value); 
     notify(); 
    } 
    public synchronized int dequeue() { 
     try { 
      while (queue.isEmpty()) { 
       System.out.println(); 
       System.out.println("Queue is empty, please wait...."); 
       wait(); 
      } 
     } 
     catch (InterruptedException e) { } 
     int data = ((SynchronizedQueue) queue).dequeue(); 
     notify(); 
     return data; 
    } 
} 

主程序Ch10_3.java：

class Producer extends Thread { 
    public int count = 0; 
    public void run() { 
     int value; 
     while (Ch10_3.isRunning) { 
      value = (int)(Math.random()*100); 
      Ch10_3.squeue.enqueue(value); 
      System.out.print(">" + value + "]"); 
      count++; 
      try { 
       Thread.sleep((int)(Math.random()*100)); 
      } 
      catch(InterruptedException e) { } 
     } 
     System.out.println("\n" + Thread.currentThread() + "Producer thread end."); 
    } 
} 

class Consumer extends Thread { 
    public int count = 0; 
    public void run() { 
     int data; 
     while (Ch10_3.isRunning) { 
      data = Ch10_3.squeue.dequeue(); 
      System.out.println("[" + data + ">"); 
      count++; 
      try { 
       Thread.sleep((int)(Math.random()*100)); 
      } 
      catch(InterruptedException e) { } 
     } 
     System.out.println("\n" + Thread.currentThread() + "Consumer thread end."); 
    } 
} 

public class Ch10_3 { 
    static final int MAXITEMS = 10; 
    static SynchonizedQueue squeue = new SynchronizedQueue(); 
    static boolean isRunning = true; 

    public static void main(String[] args) { 
     Producer producer = new Producer(); 
     Consumer consumer = new Consumer(); 

     producer.start(); consumer.start(); 
     while (true) 
      if (producer.count >= MAXITEMS && producer.count == consumer.count) 
      { isRunning = false; break; } 
    } 
} 

錯誤消息：

Exception in thread "main" java.lang.Error: Unresolved compilation problem: at Ch10_3.main(Ch10_3.java:41)

Answer 1

在從enqueue和dequeue方法catch塊構成SynchronizedQueue你試圖鑄queue構件屬性，是Queue類型的，以SynchronizedQueue類。

在SynchronizedQueue.enqueue()我們：

((SynchronizedQueue) queue).enqueue(value); 

既然有Queue和SynchronizedQueue編譯器之間沒有關係給出一個編譯錯誤。你應該刪除演員。

但是，最好的解決方案是使用JAVA SDK中提供的java.util.concurrent.BlockingQueue實現，它將爲您處理所有的同步部分。