First Non-Repeated Character using stream in java

In this example, we will learn how we can find first non-repeated character using stream so first we will go oversteps how to solve this problem.

Step 1: Iterate all the character from input stream
Step 2: Now we will count character occurrence and will store this result into LinkedHashMap, why we have used LinkedHashmap to store this occurrence because we have to maintain order.
Step 3: Find first non-repeated character – This we can achieve by iterating HashMap and print key of map when occurrence count is 1.

Please find below program for this:-

import java.util.LinkedHashMap;
import java.util.Map;

public class FirstNonRepeatedCharacter {

public static Character firstNonRepeatedCharacter(String input) {
Map<Character, Long> charCountMap = input.chars() // This converts the string into a stream of characters.
.mapToObj(c -> (char) c)
.collect(Collectors.groupingBy(c -> c, LinkedHashMap::new, Collectors.counting()));//his groups the characters and counts their occurrences, storing the result in a LinkedHashMap to maintain the order of insertion.

return charCountMap.entrySet()
.stream()
.filter(entry -> entry.getValue() == 1)//This filters the entries where the character count is 1.
.map(Map.Entry::getKey)
.findFirst()// This retrieves the first character that matches the condition.
.orElse(null);
}

public static void main(String[] args) {
String input = "swiss";
Character result = firstNonRepeatedCharacter(input);

if (result != null) {
System.out.println("The first non-repeated character is: " + result);
} else {
System.out.println("There are no non-repeated characters.");
}
}
}