Java Program to Find Duplicate Words in a String

In this article, we will walk you through a Java program that identifies duplicate words in a given string.

The Strategy

• Convert the string into an array of words. 
• Use a map (e.g., HashMap) to maintain the frequency count of each word. 
• Traverse through the array of words. Update the word count on the map. 
• After storing the counts, traverse the map to identify words with a frequency greater than one.

Java Program to Find Duplicate Words in a String

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

public class DuplicateWordFinder {

    public static void main(String[] args) {
        String sentence = "Java is a programming language and Java is also a platform";

        System.out.println("Duplicate words in the string are:");
        findDuplicateWords(sentence);
    }

    public static void findDuplicateWords(String str) {
        String[] words = str.split(" ");
        Map<String, Integer> wordCountMap = new HashMap<>();

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

        for (Map.Entry<String, Integer> entry : wordCountMap.entrySet()) {
            if (entry.getValue() > 1) {
                System.out.println(entry.getKey() + ": " + entry.getValue() + " times");
            }
        }
    }
}

Output:

Duplicate words in the string are:
a: 2 times
java: 2 times
is: 2 times

Step-by-Step Explanation: 

Setting Up the String: 

 String sentence = "Java is a programming language and Java is also a platform";

Here, we've initialized a string named sentence. Our aim is to find duplicate words in this sentence.

Converting the String into an Array of Words:

        String[] words = str.split(" ");

Using the split method of the String class, we can split the string into an array of words based on spaces. 

Initializing the Word Count Map: 

        Map<String, Integer> wordCountMap = new HashMap<>();

We'll use a HashMap to store the frequency count of each word in the string. 

Populating the Map with Word Counts:

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

We iterate through each word in the word array. We convert the word to lowercase (to ensure the comparison is case-insensitive) and then update its count in the wordCountMap. 

Identifying and Printing Duplicate Words: 

        for (Map.Entry<String, Integer> entry : wordCountMap.entrySet()) {
            if (entry.getValue() > 1) {
                System.out.println(entry.getKey() + ": " + entry.getValue() + " times");
            }
        }

We then iterate through the map. For each entry, if the count (value) is greater than one, we print the word (key) and its count.

Conclusion

Identifying duplicate words in a string is an essential text analysis task that introduces beginners to string manipulation, arrays, and the use of data structures like HashMap in Java. This guide illustrates a clear and efficient approach to solving this common problem. As you delve deeper into Java and other programming languages, you'll encounter more complex tasks and challenges.

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