Java OCA OCP Practice Question 3072

Question

Given: 

1. import java.util.*;  
2. public class Main {  
3.   public static void main(String[] args) {  
4.     PriorityQueue<String> pq = new PriorityQueue<String>();  
5.     pq.add("4");  
6.     pq.add("7");  
7.     pq.add("2");  
8.     // insert code here  
9. } }

Which code fragment(s), inserted independently at line 8, produce the output "2-4-7-"?

(Choose all that apply.) 

A.  Iterator it2 = pq.iterator();  
    while(it2.hasNext()) System.out.print(it2.next() + "-");   
    System.out.println(); //from w w w.  j a  v  a  2  s.c  o  m

B.  Arrays.sort(pq.toArray());  
    Iterator it3 = pq.iterator();  
    while(it3.hasNext()) System.out.print(it3.next() + "-");   
    System.out.println(); 

C.  Object[] pqa = pq.toArray();  
    Arrays.sort(pqa);  
    for(Object o: pqa) System.out.print(o + "-");   
    System.out.println(); 

D.  String s = pq.poll();   
    while (s != null) {  
      System.out.print(s + "-");  
      s = pq.poll();  
    } 

E.  String s = pq.peek();  
    while (s != null) {  
      System.out.print(s + "-");  
      s = pq.peek();  
    }  



C and D

Note

C and D are correct ways to determine how elements in the PriorityQueue would be prioritized, although D consumes the queue in the process.

A is incorrect because the Iterator for PriorityQueue does NOT guarantee a sorted result.

B is incorrect because the toArray() method creates a new array, it doesn't change the existing array.

E is incorrect because peek() only looks at a queue's "first" element, it doesn't consume it, so an infinite loop is created.

Note: If you didn't get answer A that's okay.

Answer A might be a little bit on the trivia end of the spectrum.

So if you got this question correct except for answer A, give yourself full credit.




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