250+ TOP MCQs on Java.util – Maps and Answers [2024]

Java MCQs 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

Answer: b
Clarification: None.

2. Which of these classes provide implementation of map interface?
a) ArrayList
b) HashMap
c) LinkedList
d) DynamicList

Answer: b
Clarification: 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
Clarification: 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()

Answer: b
Clarification: 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()

Answer: d
Clarification: 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
Clarification: 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}

Answer: d
Clarification: 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]

Answer: a
Clarification: 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

Answer: b
Clarification: 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]

Answer: d
Clarification: 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].

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