Example: CharacterFrequencyUsingMap in Java

// CharacterFrequencyUsingMap
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

// Main class containing the entry point of the program
public class Main {
    public static void main(String[] args) {
        // Step 1: Initialize a Scanner to read input from the console
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter a string: ");
        String inputString = scanner.nextLine(); // Read the entire line of input
        scanner.close(); // Close the scanner to release resources

        // Step 2: Create a HashMap to store character frequencies
        // Keys will be characters, and values will be their counts (integers)
        Map<Character, Integer> charFrequencyMap = new HashMap<>();

        // Step 3: Iterate through each character of the input string
        for (char ch : inputString.toCharArray()) {
            // Step 4: For each character, update its count in the map
            // getOrDefault(key, defaultValue) returns the value for the key,
            // or defaultValue if the key is not present.
            // We then increment this count and put it back into the map.
            charFrequencyMap.put(ch, charFrequencyMap.getOrDefault(ch, 0) + 1);
        }

        // Step 5: Print the character frequencies
        System.out.println("Character frequencies:");
        for (Map.Entry<Character, Integer> entry : charFrequencyMap.entrySet()) {
            System.out.println("'" + entry.getKey() + "': " + entry.getValue());
        }
    }
}