Collections Interface - Java Questions & Answers

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

Answer: d
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

Answer: b
Explanation: None.

3. Which of these interface is not a part of Java’s collection framework?
a) List
b) Set
c) SortedMap
d) SortedList
View Answer

Answer: d
Explanation: SortedList is not a part of collection framework.

4. Which of these interface must contain a unique element?
a) Set
b) List
c) Array
d) Collection
View Answer

Answer: a
Explanation: Set interface extends collection interface to handle sets, which must contain unique elements.

5. Which of these is Basic interface that all other interface inherits?
a) Set
b) Array
c) List
d) Collection
View Answer

Answer: d
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

6. What is the output of this 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

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.
Output:
$ javac Maps.java
$ java Maps
[A=1, B=2, C=3].

7. What is the output of this program?

```
    import java.util.*;
```
```
    class vector 
```
```
    {
```

        public static void main(String args[])

```
        {
```

            Vector obj = new Vector(4,2);

            obj.addElement(new Integer(3));

            obj.addElement(new Integer(2));

            obj.addElement(new Integer(5));

```
            obj.removeAll(obj);
```

            System.out.println(obj.isEmpty());

```
        }
```
```
    }
```

a) 0
b) 1
c) true
d) false
View Answer

Answer: c
Explanation: firstly elements 3, 2, 5 are entered in the vector obj, but when obj.removeAll(obj); is executed all the elements are deleted and vector is empty, hence obj.isEmpty() returns true.
Output:
$ javac vector.java
$ java vector
true

8. 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

Answer: a
Explanation: Arrays.sort(array) method sorts the array into 1,2,3,4,5.
Output:
$ javac Array.java
$ java Array
12345

9. What is the output of this program?

```
    import java.util.*;
```
```
    class vector 
```
```
    {
```

        public static void main(String args[])

```
        {
```

            Vector obj = new Vector(4,2);

            obj.addElement(new Integer(3));

            obj.addElement(new Integer(2));

            obj.addElement(new Integer(5));

```
            obj.removeAll(obj);
```

            System.out.println(obj.isEmpty());

```
        }
```
```
    }
```

a) 0
b) 1
c) true
d) false
View Answer

10. What is the output of this program?

```
    import java.util.*;
```
```
    class Bitset 
```
```
    {
```

        public static void main(String args[])

```
        {
```
```
            BitSet obj = new BitSet(5);
```
```
            for (int i = 0; i < 5; ++i)
```
```
                obj.set(i);
```
```
            obj.clear(2);
```
```
            System.out.print(obj);
```
```
        }
```
```
    }
```

a) {0, 1, 3, 4}
b) {0, 1, 2, 4}
c) {0, 1, 2, 3, 4}
d) {0, 0, 0, 3, 4}
View Answer

Answer: a
Explanation: None.
Output:
$ javac Bitset.java
$ java Bitset
{0, 1, 3, 4}

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