This section of our 1000+ Java MCQs focuses on collection framework of Java Programming Language.
1. Which of these interface declares core method that all collections will have?
a) set
b) EventListner
c) Comparator
d) Collection
View Answer
Explanation: Collection interfaces defines core methods that all the collections like set, map, arrays etc will have.
2. Which of these interface handle sequences?
a) Set
b) List
c) Comparator
d) Collection
View Answer
Explanation: None.
3. Which of this interface must contain a unique element?
a) Set
b) List
c) Array
d) Collection
View Answer
Explanation: Set interface extends collection interface to handle sets, which must contain unique elements.
4. Which of these is a Basic interface that all other interface inherits?
a) Set
b) Array
c) List
d) Collection
View Answer
Explanation: Collection interface is inherited by all other interfaces like Set, Array, Map etc. It defines core methods that all the collections like set, map, arrays etc will have
5. Which of these is static variable defined in Collections?
a) EMPTY_SET
b) EMPTY_LIST
c) EMPTY_MAP
d) All of the mentioned
View Answer
Explanation: None.
6. What is the output of this program?
import java.util.*;
class Array
{public static void main(String args[])
{int array[] = new int [5];
for (int i = 5; i > 0; i--)
array[5 - i] = i;
Arrays.sort(array);
for (int i = 0; i < 5; ++i)
System.out.print(array[i]);;
}}
a) 12345
b) 54321
c) 1234
d) 5432
View Answer
Explanation: Arrays.sort(array) method sorts the array into 1,2,3,4,5.
Output:
$ javac Array.java $ java Array 12345
7. What is the output of this program?
import java.util.*;
class Collection_Algos{public static void main(String args[])
{LinkedList list = new LinkedList();
list.add(new Integer(2));
list.add(new Integer(8));
list.add(new Integer(5));
list.add(new Integer(1));
Iterator i = list.iterator();
Collections.reverse(list);
Collections.sort(list);
while(i.hasNext())
System.out.print(i.next() + " ");
}}
a) 2 8 5 1
b) 1 5 8 2
c) 1 2 5 8
d) 2 1 8 5
View Answer
Explanation: Collections.sort(list) sorts the given list, the list was 2->8->5->1 after sorting it became 1->2->5->8.
Output:
$ javac Collection_Algos.java $ java Collection_Algos 1 2 5 8
8. What is the output of this program?
import java.util.*;
class Collection_Algos{public static void main(String args[])
{LinkedList list = new LinkedList();
list.add(new Integer(2));
list.add(new Integer(8));
list.add(new Integer(5));
list.add(new Integer(1));
Iterator i = list.iterator();
Collections.reverse(list);
Collections.shuffle(list);
while(i.hasNext())
System.out.print(i.next() + " ");
}}
a) 2 8 5 1
b) 1 5 8 2
c) 1 2 5 8
d) Any random order
View Answer
Explanation: shuffle – randomizes all the elements in a list.
Output:
$ javac Collection_Algos.java $ java Collection_Algos 1 5 2 8
(output will be different on your system)
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