Java Multiple Choice Questions & Answers on Java.util package Maps for Freshers

1. Which of these object stores association between keys and values?

a) Hash table
b) Map
c) Array
d) String

Answer: b

2. Which of these classes provide implementation of map interface?

a) ArrayList
b) HashMap
c) LinkedList
d) DynamicList

Answer: b

Explanation: AbstractMap, WeakHashMap, HashMap and TreeMap provide implementation of map interface.

3. Which of these method is used to remove all keys/values pair from the invoking map?

a) delete()
b) remove()
c) clear()
d) removeAll()

Answer: b

4. Which of these method Map class is used to obtain an element in the map having specified key?

a) search()
b) get()
c) set()
d) look()

Answer: b

5. Which of these methods can be used to obtain set of all keys in a map?

a) getAll()
b) getKeys()
c) keyall()
d) keySet()

Answer: d

Explanation: keySet() methods is used to get a set containing all the keys used in a map. This method provides set view of the keys in the invoking map.

6. Which of these method is used add an element and corresponding key to a map?

a) put()
b) set()
c) redo()
d) add()

Answer: a

Explanation: Maps revolve around two basic operations – get() and put(). to put a value into a map, use put(), specifying the key and the value. To obtain a value, call get() , passing the key as an argument. The value is returned,

7. What is the output of this program?

1.     import java.util.*;

2.     class Maps {

3.         public static void main(String args[]) {

4.             HashMap obj = new HashMap();

5.             obj.put("A", new Integer(1));

6.             obj.put("B", new Integer(2));

7.             obj.put("C", new Integer(3));

8.             System.out.println(obj);

9.         }

10.     }

a) {A 1, B 1, C 1}
b) {A, B, C}
c) {A-1, B-1, C-1}
d) {A=1, B=2, C=3}

Answer: d

8. What is the output of this program?

1.     import java.util.*;

2.     class Maps {

3.         public static void main(String args[]) {

4.             HashMap obj = new HashMap();

5.             obj.put("A", new Integer(1));

6.             obj.put("B", new Integer(2));

7.             obj.put("C", new Integer(3));

8.             System.out.println(obj.keySet());

9.         }

10.     }

a) [A, B, C] 

b) {A, B, C}
c) {1, 2, 3}
d) [1, 2, 3] 

Answer: a

Explanation: keySet() method returns a set containing all the keys used in the invoking map. Here keys are characters A, B & C. 1, 2, 3 are the values given to these keys.

9. What is the output of this program?

1.     import java.util.*;

2.     class Maps {

3.         public static void main(String args[]) {

4.             HashMap obj = new HashMap();

5.             obj.put("A", new Integer(1));

6.             obj.put("B", new Integer(2));

7.             obj.put("C", new Integer(3));

8.             System.out.println(obj.get("B"));

9.         }

10.     }

a) 1
b) 2
c) 3
d) null

Answer: 2

Explanation: obj.get(“B”) method is used to obtain the value associated with key “B”, which is 2.

10. What is the output of this program?

1.     import java.util.*;

2.     class Maps {

3.         public static void main(String args[]) {

4.             TreeMap obj = new TreeMap();

5.             obj.put("A", new Integer(1));

6.             obj.put("B", new Integer(2));

7.             obj.put("C", new Integer(3));

8.             System.out.println(obj.entrySet());

9.         }

10.     }

a) [A, B, C] 

b) [1, 2, 3] 

c) {A=1, B=2, C=3}

d) [A=1, B=2, C=3]

Answer: d

Explanation: obj.entrySet() method is used to obtain a set that contains the entries in the map. This method provides set view of the invoking map.