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      Question

      Consider the following Java code snippet:    

      import java.util.Collections;     import java.util.PriorityQueue;     public class HeapQuestion2 {         public static void main(String[] args) {             PriorityQueue maxHeap = new PriorityQueue(Collections.reverseOrder());             maxHeap.add(10);             maxHeap.add(5);             maxHeap.add(20);             maxHeap.add(3);             System.out.println(maxHeap.poll());             System.out.println(maxHeap.poll());         }     }     What will be the output of this program?
      A 3, 5 Correct Answer Incorrect Answer
      B 20, 10 Correct Answer Incorrect Answer
      C 10, 5 Correct Answer Incorrect Answer
      D 20, 3 Correct Answer Incorrect Answer
      E 5, 10 Correct Answer Incorrect Answer

      Solution

      By passing Collections.reverseOrder() to the PriorityQueue constructor, we create a max-heap, where the largest element has the highest priority (is at the root).     1.  maxHeap.add(10); maxHeap.add(5); maxHeap.add(20); maxHeap.add(3);         After these additions, the heap contains {20, 10, 5, 3} (conceptually, 20 is at the root).     2.  System.out.println(maxHeap.poll());         poll() removes and returns the largest element. So, 20 is removed and printed. The heap now contains {10, 5, 3}.     3.  System.out.println(maxHeap.poll());         poll() removes and returns the largest element again. So, 10 is removed and printed. The heap now contains {5, 3}.     Therefore, the output is 20, 10.

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