Count the Occurrence of Each Character in a String Using Java

In this post, we'll learn how to count the occurrence of each character in a given string using Java. This is a frequently asked question in Java coding interviews and also helps in mastering Map data structure.

🧠 Why Character Frequency?

It helps in solving many string-related problems such as anagrams, duplicates, and string compression. Understanding how to use a map to count items is a valuable skill.

1️⃣ Count Character Frequency Using HashMap

import java.util.HashMap;
import java.util.Map;

public class CharacterCount {
    public static void main(String[] args) {
        String input = "hello world";

        Map<Character, Integer> countMap = new HashMap<>();

        for (char c : input.toCharArray()) {
            if (c != ' ') { // skip spaces
                countMap.put(c, countMap.getOrDefault(c, 0) + 1);
            }
        }

        for (Map.Entry<Character, Integer> entry : countMap.entrySet()) {
            System.out.println(entry.getKey() + ": " + entry.getValue());
        }
    }
}

✅ Output

h: 1
e: 1
l: 3
o: 2
w: 1
r: 1
d: 1

📌 Interview Tip

This program is often extended to ask for the most frequent character or to ignore case sensitivity. Always clarify requirements before jumping into the code.

📚 Conclusion

Using a HashMap to count character occurrences is a fundamental technique in Java string manipulation. It's efficient and scalable even for large strings.