Find Occurrence Of Each Character From String

March 15, 2026

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Today I have released new video on "Java Interview Coding Question | Find Occurrence Of Each Character From String in Java 8 Stream API"

This is frequently asked question in Java Interview.

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package org.practice.basicprgms;

import java.util.Collections;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;

public class FindOccurencesOfEachCharacter {

	public static void main(String[] args) {
		String input = "session";
		
		// Solution 1: Using GroupingBy and Counting()
		Map<Character, Long> map = 
			input.chars()
				.mapToObj(c -> (char) c)
				.collect(Collectors.groupingBy(Function.identity(),
												Collectors.counting()));
		
		System.out.println("Using groupingBy : "+ map);

		// Solution 2: Using groupingBy and LinkedHashMap(Maintain order of Characters)
		map = input.chars()
					.mapToObj(c -> (char) c)
					.collect(Collectors.groupingBy(Function.identity(),
													LinkedHashMap::new,
													Collectors.counting()));
		
		System.out.println("Using LinkedHashMap : "+ map);	
			

		// Solution 3: Using HashMap and ForEach
		Map<Character, Integer> forEachMap = new HashMap<>();
		
		input.chars()
			.mapToObj(c -> (char) c)
			.forEach(c -> forEachMap.put(c, forEachMap.getOrDefault(c, 0) + 1));
		
		System.out.println("using forEach : "+ forEachMap);	
		

		// Solution 4: Using Collections.Frequency() method
		List<Character> charList = input.chars()
										.mapToObj(c -> (char) c)
										.collect(Collectors.toList());
		
		Map<Character, Integer> freqMap =
				charList.stream()
						.distinct()
						.collect(Collectors.toMap(c -> c, 
												  c -> Collections.frequency(charList, c)
								));
		
		System.out.println("Using Frequency : " + freqMap);
		

		// Solution 5: Using Merge() method
		Map<Character, Integer> mergeMap = new HashMap<>();
		for(char c: input.toCharArray()) {
			mergeMap.merge(c, 1, Integer::sum);
		}
		
		System.out.println("Using MergeMap : "+ mergeMap);
		
		

	}

}

Output: 
Using groupingBy : {s=3, e=1, i=1, n=1, o=1}
Using LinkedHashMap : {s=3, e=1, i=1, o=1, n=1}
using forEach : {s=3, e=1, i=1, n=1, o=1}
Using Frequency : {s=3, e=1, i=1, n=1, o=1}
Using MergeMap : {s=3, e=1, i=1, n=1, o=1}