Java的消費者/生產者

Question

public class Queue { 
    int value = 0; 
    boolean isEmpty = true; 
    public synchronized void put(int n){ 
     if (!isEmpty){ 
      try { 
       System.out.println("producer is waiting"); 
       wait(); 
      }catch (Exception e){ 
       e.printStackTrace(); 
      } 
     } 
     value += n; 
     isEmpty = false; 
     System.out.println("The number of products："+value); 
     notifyAll(); 
    } 
    public synchronized void get(){ 
     if (isEmpty){ 
      try{ 
       System.out.println("customer is waiting"); 
       wait(); 
      }catch (Exception e){ 
       e.printStackTrace(); 
      } 
     } 
     value --; 
     if(value<1){ 
      isEmpty = true; 
     } 
     System.out.println("there are "+value+" left"); 
     notifyAll(); 
    } 
} 


public class Producer extends Thread{ 
    private Queue queue; 
    public Producer(String name,Queue queue){ 
     super(name); 
     this.queue = queue; 
    } 

    @Override 
    public void run() { 
     for (int i = 0; i < 5; i++) { 
      queue.put(i+1); 
     } 
    } 

} 

public class Producer extends Thread{ 
    private Queue queue; 
    public Producer(String name,Queue queue){ 
     super(name); 
     this.queue = queue; 
    } 

    @Override 
    public void run() { 
     for (int i = 0; i < 5; i++) { 
      queue.put(i+1); 
     } 
    } 
} 


public class Main { 

    public static void main(String[] args) { 
     Queue queue = new Queue(); 
     Thread customer1 = new Customer("customer1",queue); 
     Thread producer1 = new Producer("producer1",queue); 
     customer1.setPriority(4); 
     producer1.setPriority(7); 
     producer1.start(); 
     customer1.start(); 

    } 

} 

輸出：

 
The number of products：1  
producer is waiting  
there are 0left  
customer is waiting  
The number of products：2  
producer is waiting  
there are 1left  
there are 0left  
customer is waiting  
The number of products：3  
producer is waiting  
there are 2left  
there are 1left  
there are 0left  
customer is waiting 
The number of products：4  
producer is waiting  
there are 3left  
there are 2left  
there are 1left  
there are 0left  
customer is waiting  
The number of products：5  
there are 4left  
there are 3left  
there are 2left  
there are 1left  
there are 0left  
customer is waiting 

我不知道爲什麼的輸出順序是這樣的。

爲什麼它不在輸出像

 
The number of products：3 
producer is waiting  
there are 2left  
The number of products: 6  
there are 5left    
The number of products: 10  
there are 9left  
The number of products: 15   
there are 14left 

Answer 1

的結果，我認爲這個問題是你不beeing通知後，請檢查你的病情。

你做

if (condition){ 
    wait(); 
} 
increment(); 

雖然你的線程可能會在別的方面得到通知，也不會檢查，如果條件仍然存在，或由另一個線程已經解決，做增量反正。 正確的方法是在喚醒時重新檢查您的狀況，如：

while (condition){ 
    wait(); 
} 
increment();