Java Program to check for Duplicate Characters

Program

import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import java.util.Scanner;
public class DuplicateCharactersCheck {
  public void countDuplicateChar(String string){ 
    Map<Character, Integer> countMap = new HashMap<Character, Integer>(); 
    char[] characters = string.toCharArray(); 
    for(Character ch:characters){
      if(countMap.containsKey(ch)){
         countMap.put(ch, countMap.get(ch)+1);
      } else {
         countMap.put(ch, 1);
        }
    }
    Set<Character> keys = countMap.keySet(); 
    for(Character ch:keys){    
        if(countMap.get(ch) > 1) {
            System.out.println(ch+" "+countMap.get(ch));     
        } 
        else{
          System.out.println("No Duplicate characters present");  
        }     
    }
  }
  public static void main(String[] args){
    DuplicateCharactersCheck duplicateCharactersCheck = new DuplicateCharactersCheck();
    System.out.println("Example String 1: www.oodlescoop.com");   
    duplicateCharactersCheck.countDuplicateChar("www.oodlescoop.com");
    System.out.println("\nExample String 2: Engineering");   
    duplicateCharactersCheck.countDuplicateChar("Engineering"); 
    Scanner reader = new Scanner(System.in);
    System.out.println("Enter a string: ");
    String enteredString = reader.next();
    System.out.println("Duplicate Count for string : "+ enteredString +" is: ");
    duplicateCharactersCheck.countDuplicateChar(enteredString); 
    }
}

This program identifies and counts duplicate characters in a given string using a HashMap.

1. Input:

   • The program takes predefined strings and user input to analyze duplicate characters.

2. Logic:

   • HashMap is used to store characters and their frequencies:
     • Key: A character from the string.
     • Value: The count of occurrences of the character.

3. Steps:

   • Convert the input string to a character array using toCharArray().
   • Loop through each character:
     • If the character already exists in the HashMap, increment its value.
     • Otherwise, add the character to the HashMap with an initial count of 1.

4. Check for Duplicates:

   • Iterate through the HashMap:
     • If a character's count is greater than 1, print the character and its frequency.
     • Otherwise, print that no duplicates are present.

5. Output:

   • For each string, duplicate characters and their counts are displayed.
   • Example:

     Example String 1: www.oodlescoop.com
     w 3
     o 5
     l 1
     e 1
     s 1
     c 2
     p 1
     m 1
     

6. Usage of Set:

   • The keySet() method retrieves all unique characters (keys) in the map.

7. Interactive Input:

   • The program prompts the user to enter a string and displays the duplicate character count for the input.

Features:

• HashMap Efficiency:
  • Provides quick lookups and updates for character counts.
• Character-by-Character Analysis:
  • Ensures each character is processed only once.
• Flexibility:
  • Works with any string input, including spaces and special characters.

Example Execution:

• Input:

  Example String 2: Engineering
  

• Process:
  • Counts:
    • e: 3 times
    • n: 3 times
    • i: 2 times
    • g: 2 times
  • Output:

    e 3
    n 3
    i 2
    g 2
    

Use Case:

This program can be used for:

• Validating strings for duplicate characters.
• Data analysis in text processing.
• Debugging or identifying redundant characters in user input.

Output

$ javac DuplicateCharactersCheck.java
$ java DuplicateCharactersCheck
Example String 1: www.oodlescoop.com
c 2
w 3
. 2
o 5
Example String 2: Engineering
e 2
g 2
i 2
n 3
Enter a string:
Programming
Duplicate Count for string : Programming is:
r 2
g 2
m 2