Find the first non-repeating character in a string using Java 8

In this tutorial, we will learn “Find the first non-repeating character in a string using Java 8?”. In order to do that, we are going to leverage the Stream API along with the Collectors.groupingBy collector.

Find the first non-repeated character in a string using Java 8

Find the first non-repeating character in a string using Java 8 Share on X

/**
 * Using Java 8, Find the first non-repeating character in a string
 * @author Deepak Verma
 *
 */

import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Optional;
import java.util.function.Function;
import java.util.stream.Collectors;

public class Find_first_non_repeating_character_in_string_Java8Stream {

	public static void main(String[] args) {
        String inputString = "Techndeck";
        Optional<Character> ourcome = findFirstNonRepeatedCharacter(inputString);
        
        ourcome.ifPresentOrElse(
            character -> System.out.println("First Non-Repeated Character: " + character),
            () -> System.out.println("There is No non-repeated character present in the string.")
        );
    }

    public static Optional<Character> findFirstNonRepeatedCharacter(String inputStr) {
        Map<Character, Long> charCountingMap = inputStr.chars()
                .mapToObj(c -> (char) c)
                .collect(
                        Collectors.groupingBy(
                                Function.identity(),
                                LinkedHashMap::new,
                                Collectors.counting()
                        )
                );

        return charCountingMap.entrySet().stream()
                .filter(entry -> entry.getValue() == 1)
                .map(Map.Entry::getKey)
                .findFirst();
    }
}

Output:

First Non-Repeated Character: T

check if text or string present in a file using java 8

The code above defines a method findFirstNonRepeatedCharacter that takes a string as input and returns an Optional<Character> which represents the first non-repeated character.

Steps:

1. Convert the input string to a stream of characters using chars().
2. Convert each character to a Character object.
3. Use Collectors.groupingBy to group the characters by their counts in a LinkedHashMap.
4. Filter the entries to find characters with a count of 1.
5. Map the entry set to characters.
6. Use findFirst to get the first non-repeated character.

skip method java 8 stream

Find the first non-repeating character in a string using Java 8 Share on X

Do you like this Post? – then check my other helpful posts:

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• How to check if Number is Prime or not using Streams
• Retrieve Even/Odd Numbers within the Range using Java 8 Streams
• How to add/sum up the ArrayList integers using Java8 Streams
• Generate Prime Numbers in Java 8 using Streams
• Comparator example – Collections sort with/without Lambda in Java 8
• How to pass function as a parameter in a method in Java 8?
• Remove duplicates from ArrayList in Java 8
• ForEach examples for Map/List in Java 8

Other Useful References:

• java.util.stream by Oracle