Core Java Interview Question

What is the Collections API?

The Collections API is a set of classes and interfaces that support operations on
collections of objects.

What is the List interface?

The List interface provides support for ordered collections of objects.

What is the Vector class?

The Vector class provides the capability to implement a growable array of objects

What is an Iterator interface?

The Iterator interface is used to step through the elements of a Collection.

What is HashMap and Map?

Map is Interface and Hashmap is class that implements this interface.

import java.util.*;

public class MapExample {

public static void main(String args[]) {

Map map = new HashMap();

Integer ONE = new Integer(1);

for (int i=0, n=args.length; i<n; i++) {

String key = args[i];

Integer frequency = (Integer)map.get(key);

if (frequency == null) {

frequency = ONE;

} else {

int value = frequency.intValue();

frequency = new Integer(value + 1);

}

map.put(key, frequency);

}

System.out.println(map);

Map sortedMap = new TreeMap(map);

System.out.println(sortedMap);

}

}

What is Map.Entry interface ?

The entrySet() method of Map returns a collection of objects that implement the

Map.Entry interface. Each object in the collection is a specific key-value pair in the

underlying Map .

What is the difference b/w Iterator and ListIterator?

Iterator : Enables you to cycle through a collection in the forward direction only, for obtaining or removing elements

ListIterator : It extends Iterator, allow bidirectional traversal of list and the modification of elements

 

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