This section of our 1000+ Java MCQs focuses on Maps of Java Programming Language.
1. Which of these object stores association between keys and values?
a) Hash table
b) Map
c) Array
d) String
View Answer
Explanation: None.
2. Which of these classes provide implementation of map interface?
a) ArrayList
b) HashMap
c) LinkedList
d) DynamicList
View Answer
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()
View Answer
Explanation: None.
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()
View Answer
Explanation: None.
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()
View Answer
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()
View Answer
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 will be the output of the following Java program?
import java.util.*;
class Maps{public static void main(String args[])
{HashMap obj = new HashMap();
obj.put("A", new Integer(1));
obj.put("B", new Integer(2));
obj.put("C", new Integer(3));
System.out.println(obj);
}}
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}
View Answer
Explanation: None.
Output:
$ javac Maps.java $ java Maps {A=1, B=2, C=3}
8. What will be the output of the following Java program?
import java.util.*;
class Maps{public static void main(String args[])
{HashMap obj = new HashMap();
obj.put("A", new Integer(1));
obj.put("B", new Integer(2));
obj.put("C", new Integer(3));
System.out.println(obj.keySet());
}}
a) [A, B, C]
b) {A, B, C}
c) {1, 2, 3}
d) [1, 2, 3]
View Answer
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.
Output:
$ javac Maps.java $ java Maps [A, B, C].
9. What will be the output of the following Java program?
import java.util.*;
class Maps{public static void main(String args[])
{HashMap obj = new HashMap();
obj.put("A", new Integer(1));
obj.put("B", new Integer(2));
obj.put("C", new Integer(3));
System.out.println(obj.get("B"));
}}
a) 1
b) 2
c) 3
d) null
View Answer
Explanation: obj.get(“B”) method is used to obtain the value associated with key “B”, which is 2.
Output:
$ javac Maps.java $ java Maps 2
10. What will be the output of the following Java program?
import java.util.*;
class Maps{public static void main(String args[])
{TreeMap obj = new TreeMap();
obj.put("A", new Integer(1));
obj.put("B", new Integer(2));
obj.put("C", new Integer(3));
System.out.println(obj.entrySet());
}}
a) [A, B, C]
b) [1, 2, 3]
c) {A=1, B=2, C=3}
d) [A=1, B=2, C=3]
View Answer
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.
Output:
$ javac Maps.java $ java Maps [A=1, B=2, C=3].
Sanfoundry Global Education & Learning Series – Java Programming Language.
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