Print content of priority queue

5
votes

How do I make the print_queue work properly in Java? This is my own implementation of a queue.

Using Iterator() works fine, except it prints numbers in random order.

package data_structures_java ;
import java.util.Iterator;
import java.util.PriorityQueue ;
import java.util.* ;
public class Queue_implementation {
 
    PriorityQueue<Integer> actual_queue ;
    
    public Queue_implementation(){
        actual_queue = new PriorityQueue<Integer>() ;
        
    }
    
    public  void add(int num){
        actual_queue.add(num) ;
    }
    
    public int remove(){
          return actual_queue.remove() ;          
    }
    
    public int peek(){
        if( actual_queue.isEmpty()) return -1 ;
        else return actual_queue.peek() ;
    }
    
    public int element(){
        return actual_queue.element() ;
    }
    
    public void print_queue(){      
        PriorityQueue<Integer>copy = new PriorityQueue<Integer>();
        copy.addAll(actual_queue) ;        
        Iterator<Integer> through = actual_queue.iterator() ;
        while(through.hasNext() ) {
                System.out.print(through.next() + " ") ;
        }
        System.out.println() ;
                
        actual_queue.addAll(copy) ;
        
    }
    public static void main(String[] args) {            
        Queue_implementation x = new Queue_implementation() ;
        x.add(10) ;
        x.add(9) ;
        x.add(8) ;
        x.add(7) ;
        x.add(6) ;
        x.print_queue() ;
    }

}

I tried to use toArray() but it returns Object[], which I don't know how to traverse:

Object[] queue_object_array = x.toArray() ;
Arrays.sort(queue_object_array) ;
3
javaqueuepriority-queue
Is your Queue supposed to be a Queue or is is supposed to be a PriorityQueue? They do two different things. - Will Newton
@WillNewton, just queue actually , but i m using std.priority queue from java api - ERJAN

3 Answers

9
votes

Using Iterator() works fine, except it prints numbers in random order.

That's exactly what it says it will do in the Javadoc. The only way to get the ordering in the PriorityQueue is to use the poll() or remove() methods.

4
votes

One line solution: it is useful when you need to fast debug.

System.out.println(Arrays.toString(priorityQueue.toArray()));

Edit: Another concise code:

System.out.println(priorityQueue);
1
votes

If you need to print content of priorityQueue where each element is a 2D array you can try using:

System.out.println(Arrays.deepToString(priorityQueue.toArray());

If it's a 1D array:

System.out.println(Arrays.toString(priorityQueue.toArray());