Write a Java Program to count the frequency of each word in a given string using a HashMap.

Question

Accepted Answer

Approach:
The solution splits the input string into individual words using whitespace as the delimiter. A HashMap is then used to store each word as the key and its occurrence count as the value. If a word already exists in the map, its count is incremented; otherwise, it is added with an initial count of 1.

HashMap provides constant-time average lookup and update operations, making it an efficient choice for frequency counting problems.

Java Solution:
```
import java.util.HashMap;
import java.util.Map;

public class WordCountUsingHashMap {

public static void main(String[] args) {
        String input = "Java is powerful and Java is popular";

String[] words = input.split("\s+");

Map wordCountMap = new HashMap();

for (String word : words) {
            wordCountMap.put(
                    word,
```
                    wordCountMap.getOrDefault(word, 0) + 1
```
            );
        }

for (Map.Entry entry : wordCountMap.entrySet()) {
            System.out.println(entry.getKey() + " : " + entry.getValue());
        }
    }
}
```
Output:
Java : 2
is : 2
powerful : 1
and : 1
popular : 1

Time Complexity:
O(n), where n is the number of words in the input string. Each word is processed exactly once.

Space Complexity:
O(k), where k is the number of unique words stored in the HashMap.

Key Interview Points:
• HashMap is commonly used for frequency counting problems because of its O(1) average lookup and insertion time.
• The getOrDefault() method simplifies the logic for handling existing and new words.
• A common follow-up question is to find the first non-repeated word or the most frequently occurring word in the string.