🎓 Top 15 Udemy Courses (80-90% Discount): My Udemy Courses - Ramesh Fadatare — All my Udemy courses are real-time and project oriented courses.

▶️ Subscribe to My YouTube Channel (178K+ subscribers): Java Guides on YouTube

▶️ For AI, ChatGPT, Web, Tech, and Generative AI, subscribe to another channel: Ramesh Fadatare on YouTube

Introduction

Counting duplicate characters in a string is a common text-processing task. In this guide, we'll write a Java program that takes a string as input and counts the number of duplicate characters.

Problem Statement

Create a Java program that:

Takes a string input from the user.
Counts the number of characters that appear more than once in the string.
Displays the duplicate characters and their counts.

Example 1:

Input: "programming"
Output: {r=2, g=2, m=2}

Example 2:

Input: "hello"
Output: {l=2}

Example 3:

Input: "abcd"
Output: {} (No duplicates)

Solution Steps

Input String: Accept a string input from the user.
Normalize the String: Convert the string to lowercase to make the comparison case-insensitive.
Count Character Frequencies: Use a HashMap to store the frequency of each character in the string.
Identify Duplicates: Traverse the map to identify characters that have a frequency greater than 1.
Output the Result: Display the duplicate characters and their counts.

Java Program

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

/**
 * Java Program to Count Duplicate Characters in a String
 * Author: https://www.javaguides.net/
 */
public class DuplicateCharacterCounter {

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

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

        // Step 2: Normalize the String
        input = input.toLowerCase();

        // Step 3: Count Character Frequencies
        Map<Character, Integer> charCountMap = new HashMap<>();
        for (char c : input.toCharArray()) {
            charCountMap.put(c, charCountMap.getOrDefault(c, 0) + 1);
        }

        // Step 4: Identify Duplicates
        Map<Character, Integer> duplicates = new HashMap<>();
        for (Map.Entry<Character, Integer> entry : charCountMap.entrySet()) {
            if (entry.getValue() > 1) {
                duplicates.put(entry.getKey(), entry.getValue());
            }
        }

        // Step 5: Output the Result
        System.out.println("Duplicate Characters: " + duplicates);
    }
}

Explanation

Step 1: Input String

The program prompts the user to enter a string.

Step 2: Normalize the String

The string is converted to lowercase to ensure that character comparisons are case-insensitive.

Step 3: Count Character Frequencies

A HashMap is used to store the frequency of each character in the string. As the string is iterated, each character's count is updated in the map.

Step 4: Identify Duplicates

The program iterates over the HashMap to identify characters that have a frequency greater than 1. These characters are stored in another HashMap called duplicates.

Step 5: Output the Result

The program prints the duplicate characters and their counts.

Output Examples

Example 1:

Enter a string: programming
Duplicate Characters: {r=2, g=2, m=2}

Example 2:

Enter a string: hello
Duplicate Characters: {l=2}

Example 3:

Enter a string: abcd
Duplicate Characters: {}

Conclusion

This Java program efficiently counts and displays duplicate characters in a string. By using a HashMap to track the frequency of each character, the program can easily identify and report characters that appear more than once. This method is straightforward and can be easily modified to suit various string processing needs.

My Top and Bestseller Udemy Courses. The sale is going on with a 70 - 80% discount. The discount coupon has been added to each course below:

Spring Boot + RabbitMQ Course - The Practical Guide

Related Java Programs with Output and Explanations

Java Program to Count Duplicate Characters in a String

Introduction

Problem Statement

Example 1:

Example 2:

Example 3:

Solution Steps

Java Program

Explanation

Step 1: Input String

Step 2: Normalize the String

Step 3: Count Character Frequencies

Step 4: Identify Duplicates

Step 5: Output the Result

Output Examples

Example 1:

Example 2:

Example 3:

Conclusion

My Top and Bestseller Udemy Courses. The sale is going on with a 70 - 80% discount. The discount coupon has been added to each course below:

Build REST APIs with Spring Boot 4, Spring Security 7, and JWT

[NEW] Learn Apache Maven with IntelliJ IDEA and Java 25

ChatGPT + Generative AI + Prompt Engineering for Beginners

Spring 7 and Spring Boot 4 for Beginners (Includes 8 Projects)

Building Real-Time REST APIs with Spring Boot - Blog App

Building Microservices with Spring Boot and Spring Cloud

Java Full-Stack Developer Course with Spring Boot and React JS

Build 5 Spring Boot Projects with Java: Line-by-Line Coding

Testing Spring Boot Application with JUnit and Mockito

Spring Boot Thymeleaf Real-Time Web Application - Blog App

Master Spring Data JPA with Hibernate

Spring Boot + Apache Kafka Course - The Practical Guide

Java Testing: Mastering JUnit 5 Framework

Reactive Programming in Java: Spring WebFlux and Testing

Spring Boot + RabbitMQ Course - The Practical Guide

Functional Programming in Java (Includes Java Collections)

ChatGPT for Java Developers: Boost Your Productivity with AI

Related Java Programs with Output and Explanations

Comments

Post a Comment

Spring Boot 3 Paid Course Published for Free on my Java Guides YouTube Channel

Spring Boot 3 Paid Course Published for Free
on my Java Guides YouTube Channel