Output of Java programs | Set 13 (Collections)

Prerequisite – Collections in Java

1) What is the output of the following program?

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import java.util.*;
  
public class priorityQueue
{
    public static void main(String[] args)
    {
        PriorityQueue<Integer> queue =
                            new PriorityQueue<>();
        queue.add(11);
        queue.add(10);
        queue.add(22);
        queue.add(5);
        queue.add(12);
        queue.add(2);
  
        while (queue.isEmpty() == false)
            System.out.printf("%d ", queue.remove());
  
        System.out.println("\n");
    }
}

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a) 11 10 22 5 12 2
b) 2 12 5 22 10 11
c) 2 5 10 11 12 22
d) 22 12 11 10 5 2
Ans. (c)
Explanation: Priority queue always outputs the minimum element from the queue when remove() method is called, no matter what the sequence of input is.

 

2) What is the output of the following program?



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import java.util.*;
  
public class Treeset
{
    public static void main(String[] args)
    {
        TreeSet<String> treeSet = new TreeSet<>();
  
        treeSet.add("Geeks");
        treeSet.add("for");
        treeSet.add("Geeks");
        treeSet.add("GeeksforGeeks");
  
        for (String temp : treeSet)
            System.out.printf(temp + " ");
  
        System.out.println("\n");
    }
}

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a) Geeks for Geeks GeeksforGeeks
b) Geeks for GeeksforGeeks
c) Geeks GeeksforGeeks for
d) for GeeksforGeeks Geeks

Ans. (c)
Explanation: A TreeSet sorts the data in ascending order that is inserted in it. Therefore, the output string contains all the strings arranged in ascending order. A TreeSet does not contain any duplicate element as it is a set. So in the output, there is just a single occurance of string ‘Geeks’.

 

3) What is the output of the following program?

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import java.util.*;
  
public class linkedList
{
    public static void main(String[] args)
    {
        List<String> list1 = new LinkedList<>();
        list1.add("Geeks");
        list1.add("for");
        list1.add("Geeks");
        list1.add("GFG");
        list1.add("GeeksforGeeks");
  
        List<String> list2 = new LinkedList<>();
        list2.add("Geeks");
  
        list1.removeAll(list2);
  
        for (String temp : list1)
            System.out.printf(temp + " ");
  
        System.out.println();
    }
}

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a) for Geeks GFG GeeksforGeeks
b) for GFG GeeksforGeeks
c) for GFG for
d) for GFG GeeksforGeeks

Ans. (d)
Explanation: list1.removeAll(list2) function deletes all the occurance of string in list2 from list1. Here, the string ‘Geeks’ appears in list2, so all the nodes of linked list in list1 that contains ‘Geeks’ as its data is removed from list1.

 
4) Which of the given choices is a possible output ?

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import java.util.*;
  
public class hashSet
{
    public static void main(String[] args)
    {
        HashSet<String> hashSet = new HashSet<>();
        hashSet.add("Geeks");
        hashSet.add("for");
        hashSet.add("Geeks");
        hashSet.add("GeeksforGeeks");
  
        System.out.println(hashSet);
  
    }
}

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a) [Geeks, for, Geeks, GeeksforGeeks]
b) [GeeksforGeeks, Geeks, for]
Ans. (b)
Explanation: A HashSet is a set and as a set doesn’t contain any duplicate element therefore, the string ‘Geeks’ appears only once in the output.

 

5) What is the output of the following program?

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import java.util.*;
  
public class stack
{
    public static void main(String[] args)
    {
        List<String> list = new LinkedList<>();
        list.add("Geeks");
        list.add("for");
        list.add("Geeks");
        list.add("GeeksforGeeks");
        Iterator<Integer> iter = list.iterator();
  
        while (iter.hasNext())
            System.out.printf(iter.next() + " ");
  
        System.out.println();
    }
}

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a) Geeks for Geeks GeeksforGeeks
b) GeeksforGeeks Geeks for Geeks
c) Runtime Error
d) Compilation Error

Ans. (d)
Explanation: An iterator made for iterating over Integer cannot be used to iterate over String data type. Corrected program : https://ide.geeksforgeeks.org/DgeN0P

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