Java – How to uppercase every duplicate character in String ?

In this article, we will discuss steps and execution program to uppercase all duplicate characters/occurrences from given String


Uppercase duplicate character in String :


  1. Initially, create empty StringBuilder object to store all converted string
  2. first, LOWER-CASE entire original String before any operation
  3. create String[] array using space (\\s) as delimiter in split(); method of String
  4. Iterate through original String after split (Outer for-loop)
  5. while iterating, store split’ed string in temporary variable
  6. create LinkedHashSet to check/store duplicate occurrences
  7. convert temp String into character-array (char[]) using toCharArray(); method
  8. Iterate through converted char[] array (Inner for-each loop)
  9. check whether char already present in LinkedHashSet, while iterating Inner for-loop
  10. If not present, then add to LinkedHashSet using add(); method as well as StringBuilder using append(); method
  11. If present, then store duplicate character in StringBuilder after converting to UPPER-CASE
  12. add single space to StringBuilder after each iteration of Outer for-loop
  13. finally pretty print to console

package in.bench.resources.collection;

import java.util.LinkedHashSet;
import java.util.Set;

public class UpperCaseDuplicateCharacterInString {

	public static void main(String[] args) {

		// sample test string
		String testStr = "madam sss gg fff rr malayalam";
		Set<Character> lhSet = null;

		// Step 1: create StringBuilder object 
		// to store converted strings
		StringBuilder sbuilder = new StringBuilder();

		// Step 2: first, LOWER-CASE entire String before any operation
		String lowerStr = testStr.toLowerCase();

		// Step 3: create String[] using 
		// space as delimiter in split() method of String
		String[] strArray = lowerStr.split("\\s");

		// Step 4: Iterate original String after split
		for(int index=0; index < strArray.length; index++) {

			// Step 5: store it in temporary variable
			String temp = strArray[index];

			// Step 6: create LinkedHashSet to check/store duplicate
			lhSet = new LinkedHashSet<Character>();

			// Step 7: convert temp String into character-array 
			// using toCharArray() method 
			char[] chArray = temp.toCharArray();

			// Step 8: iterate through converted char[] array
			for(char ch : chArray) {

				// Step 9: check whether char already present in LHSet
				boolean checkChar = lhSet.contains(ch);

				// Step 10: if not present, then add
				if(!checkChar) {
				else {
					// Step 11: if present, then store duplicate 
					// after converting to UPPER-CASE in StringBuilder 

			// Step 12: add single space after outer for-loop
			sbuilder.append(" ");

		// Step 13: finally pretty print to console
		System.out.println("Original String  : " 
				+ testStr);
		System.out.println("\nConverted String : " 
				+ sbuilder.toString().trim());

Output :

Original String  : madam sss gg fff rr malayalam

Converted String : madAM sSS gG fFF rR malAyALAM


Happy Coding !!
Happy Learning !!

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