Java: Count duplicate characters in a String

Last update on March 17 2025 13:22:26 (UTC/GMT +8 hours)

Write a Java program to count the number of characters (alphanumeric only) that occur more than twice in a given string.

Visual Presentation:

Java String Exercises: Count duplicate characters in a String

Sample Data:

(“abcdaa”) -> 1
("Tergiversation") ->0

Sample Solution-1:

Java Code:

public class Main {
    public static void main(String[] args) {
        // Define a string 'text' with certain characters
        String text = "abcdaa";
        System.out.println("Original String: " + text); // Display the original string
        
        // Count and display the number of duplicate characters occurring more than twice in the string
        System.out.println("Number of duplicate characters in the said String (Occurs more than twice.): " + test(text));
        
        // Change the value of 'text' to another string
        text = "Tergiversation";
        System.out.println("\nOriginal String: " + text); // Display the original string
        
        // Count and display the number of duplicate characters occurring more than twice in the string
        System.out.println("Number of duplicate characters in the said String (Occurs more than twice.): " + test(text));
    }

    // Method to count duplicate characters occurring more than twice in a string
    public static int test(String text) {
        int ctr = 0; // Counter to store the count of duplicate characters
        
        // Continue looping until the length of 'text' becomes zero
        while (text.length() > 0) {
            // Check if the count of a character (after removal) is more than 2 in the string
            if (text.length() - text.replaceAll(text.charAt(0) + "", "").length() > 2) {
                ctr++; // Increment the counter if duplicate characters are found more than twice
            }
            
            // Remove all occurrences of the first character from the string 'text'
            text = text.replaceAll(text.charAt(0) + "", "");
        }
        
        return ctr; // Return the count of duplicate characters occurring more than twice
    }
}

Sample Output:

Original String: abcdaa
Number of duplicate characters in the said String (Occurs more than twice.): 1

Original String: Tergiversation
Number of duplicate characters in the said String (Occurs more than twice.): 0

Flowchart:

Flowchart: Java String Exercises - Reverses the words in a string that have odd lengths

Sample Solution-2:

Java Code:

import java.util.function.Function;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        // Define a string 'text' with certain characters
        String text = "abcdaa";
        System.out.println("Original String: " + text); // Display the original string
        
        // Count and display the number of duplicate characters occurring more than twice in the string
        System.out.println("Number of duplicate characters in the said String (Occurs more than twice.): " + test(text));
        
        // Change the value of 'text' to another string
        text = "Tergiversation";
        System.out.println("\nOriginal String: " + text); // Display the original string
        
        // Count and display the number of duplicate characters occurring more than twice in the string
        System.out.println("Number of duplicate characters in the said String (Occurs more than twice.): " + test(text));
    }

    // Method to count duplicate characters occurring more than twice in a string
    public static int test(String text) {
        return (int) text.chars() // Convert the string into an IntStream of characters
                .boxed() // Box each integer value into its corresponding Integer object
                .collect(Collectors.groupingBy(Function.identity(), Collectors.counting())) // Collect the characters into a map with their counts
                .values() // Get the values (counts) from the map
                .stream() // Convert the Collection into a Stream
                .filter(ctr -> ctr > 2) // Filter the counts to keep those occurring more than twice
                .count(); // Count the filtered occurrences
    }
}

Sample Output:

Original String: abcdaa
Number of duplicate characters in the said String (Occurs more than twice.): 1

Original String: Tergiversation
Number of duplicate characters in the said String (Occurs more than twice.): 0

Flowchart:

Flowchart: Java String Exercises - Count Occurrences Of Character

For more Practice: Solve these Related Problems:

Write a Java program to identify alphanumeric characters in a string that appear more than twice.
Write a Java program to count and display characters with a frequency greater than two in a given string.
Write a Java program to iterate through a string and count alphanumeric characters that occur over two times.
Write a Java program to tally the number of characters exceeding a specified frequency threshold in a string.

Java Code Editor:

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