Java Program to Count the Occurrences of Each Character

Introduction

Counting the occurrences of each character in a string is a common task in text processing and analysis. This guide will show you how to create a Java program that counts and displays the frequency of each character in a given string.

Problem Statement

Create a Java program that:

• Takes a string as input.
• Counts and displays the frequency of each character in the string.

Example 1:

• Input: "hello"
• Output: h: 1, e: 1, l: 2, o: 1

Example 2:

• Input: "programming"
• Output: p: 1, r: 2, o: 1, g: 2, a: 1, m: 2, i: 1, n: 1

Solution Steps

1. Prompt for Input: Use the Scanner class to read a string input from the user.
2. Use a HashMap to Track Character Frequencies: Iterate through the string and store the frequency of each character in a HashMap.
3. Display the Character Frequencies: Print the frequency of each character in the string.

Java Program

Java Program to Count the Occurrences of Each Character

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

/**
 * Java Program to Count the Occurrences of Each Character in a String
 * Author: https://www.javaguides.net/
 */
public class CharacterFrequencyCounter {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        // Step 1: Prompt the user for input
        System.out.print("Enter a string: ");
        String input = scanner.nextLine();

        // Step 2: Use a HashMap to track character frequencies
        Map<Character, Integer> charCountMap = new HashMap<>();

        for (char c : input.toCharArray()) {
            charCountMap.put(c, charCountMap.getOrDefault(c, 0) + 1);
        }

        // Step 3: Display the character frequencies
        System.out.println("Character frequencies:");
        for (Map.Entry<Character, Integer> entry : charCountMap.entrySet()) {
            System.out.println(entry.getKey() + ": " + entry.getValue());
        }
    }
}

Explanation

• Input: The program prompts the user to enter a string.
• Tracking Character Frequencies: The program uses a HashMap to count the occurrences of each character in the string. The getOrDefault method is used to increment the count if the character already exists in the map or to initialize it if it does not.
• Displaying Frequencies: The program then iterates over the HashMap to display each character and its corresponding frequency.

Output Example

Example 1:

Enter a string: hello
Character frequencies:
h: 1
e: 1
l: 2
o: 1

Example 2:

Enter a string: programming
Character frequencies:
p: 1
r: 2
o: 1
g: 2
a: 1
m: 2
i: 1
n: 1

Example 3:

Enter a string: javaguides
Character frequencies:
j: 1
a: 2
v: 1
g: 1
u: 1
i: 1
d: 1
e: 1
s: 1

Conclusion

This Java program effectively counts the occurrences of each character in a string using a HashMap. By tracking the frequency of each character, the program can display the exact number of times each character appears in the input string. This approach is practical for various text processing tasks, such as analyzing text or ensuring data integrity.