Find First Non-Repeated Character From String

February 14, 2026

Wap for Find First Non-Repeated Character From String.

Input: stress

output: t - "t" is first Non Repeated Character. I have explained through video as well. Please check out the video as well for better understanding.

package org.practice.basicprgms;

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

public class FindFirstNonRepeatedCharacter {

	public static void main(String[] args) {
		String input = "stress";
		
		// Solution 1: using indexOf() and lastIndexOf()
		Character output = input.chars()  // A - 65 a 97
							.mapToObj(c -> (char)c)
							.filter(c -> input.indexOf(c) == input.lastIndexOf(c))
							.findFirst()
							.orElse(null);
							
		System.out.println("First Non Repeated Character : "+ output);
		
		// Solution 2 : using LinkedHashMap
		output = input.chars()
					.mapToObj(ch -> (char) ch)
					.collect(Collectors.groupingBy(Function.identity(),
													LinkedHashMap::new,
													Collectors.counting()))
					.entrySet()
					.stream()
					.filter(entry -> entry.getValue() == 1)
					.map(Map.Entry :: getKey)
					.findFirst()
					.orElse(null);
		
		System.out.println("First Non Repeated Character using HashMap : "+ output);
					
		// Solution 3 : using LinkedHashMap
		Map<Character, Long> charMap =
				input.chars()
					.mapToObj(ch -> (char) ch)
					.collect(Collectors.groupingBy(Function.identity(),
													LinkedHashMap::new,
													Collectors.counting()));
		
		output = charMap.entrySet().stream()
								.filter(entry -> entry.getValue() == 1)
								.map(Map.Entry :: getKey)
								.findFirst()
								.orElse(null);
		
		System.out.println("First Non Repeated Character using HashMap second Way : "+ output);
		
		
	}

}