How to find Duplicate characters in given String in Java?

Problem Description :

Write a program in Java that prints all duplicate characters in a String. For example  "Java" has one duplicate character 'a'.

Duplicate Characters Finder

Algorithm :

We are using below steps for creating Java program.

1. Convert original String to character Array.
2. Remove all duplicate characters from String by converting String to Set.
3. Get new String by converting Set (from Step 2) to String.
4. Convert String (from Step 3) to character Array.
5. If original String and new String are same then there is no duplicate character in original String otherwise go to Step 6.
6. One by one check all characters of new String with Original String. If count > 1 it means duplicate characters present in String.

Java Program :

	package com.javamultiplex.string;
	import java.util.HashSet;
	import java.util.Iterator;
	import java.util.LinkedHashSet;
	import java.util.Scanner;
	/**
	*
	* @author Rohit Agarwal
	* @category String Interview Question
	* @Problem Print all duplicate characters in a String
	*
	*/
	public class DuplicateCharactersInString {
	public static void main(String[] args) {
	Scanner input = null;
	try {
	input = new Scanner(System.in);
	System.out.println("Enter String: ");
	String string = input.next();
	// Converting String to char array.
	char[] stringToChar = string.toCharArray();
	int orignalLength = stringToChar.length, charCount = 0;
	String newString = getStringAfterDuplicatesRemoval(stringToChar);
	// Converting String to char array.
	char[] stringToCharAfterDuplicateRemoval = newString.toCharArray();
	int newLength = stringToCharAfterDuplicateRemoval.length;
	if (string.equals(newString)) {
	System.out.println("No duplicate character available.");
	} else {
	System.out.println("Duplicate characters are: ");
	for (int i = 0; i < newLength; i++) {
	charCount = 0;
	for (int j = 0; j < orignalLength; j++) {
	if (stringToCharAfterDuplicateRemoval[i] == stringToChar[j]) {
	charCount++;
	}
	}
	if (charCount > 1) {
	System.out.println(stringToCharAfterDuplicateRemoval[i]);
	}
	}
	}
	} finally {
	if (input != null) {
	input.close();
	}
	}
	}
	// Removing duplicates by converting char Array to Set.
	private static String getStringAfterDuplicatesRemoval(char[] stringToChar) {
	HashSet<Character> set = new LinkedHashSet<>();
	String result = "";
	int orignalLength = stringToChar.length;
	for (int i = 0; i < orignalLength; i++) {
	set.add(stringToChar[i]);
	}
	Iterator<Character> iterator = set.iterator();
	while (iterator.hasNext()) {
	result += iterator.next(); // Converting Set to String
	}
	return result;
	}
	}

view raw DuplicateCharactersInString.java hosted with ❤ by GitHub

Output :

Case 1 :

Output - Duplicate characters present in given String.

Case 2 :

Output - Duplicate characters not present in given String.

References :

https://www.tutorialspoint.com/java/java_set_interface.htm

https://www.tutorialspoint.com/java/java_hashset_class.htm

https://www.tutorialspoint.com/java/java_linkedhashset_class.htm

https://www.tutorialspoint.com/java/java_strings.htm

https://www.tutorialspoint.com/java/java_using_iterator.htm

Thank you friends, I hope you have clearly understood the solution of this problem. If you have any doubt, suggestion or query please feel free to comment below. You can also discuss this solution in our forum.

Tags : Interview questions on String, Solution in Java, Duplicate characters, Iterator, HashSet, LinkedHashSet, for loop, while loop, if statement, char[] array, String functions.

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