import java.util.*; import java.util.function.Function; import java.util.stream.Collectors; public class WordFrequencyCounter { static Map countFrequencyInImperativeWay(List words) { Map frequencyMap = new HashMap<>(); for (String word : words) { if (!frequencyMap.containsKey(word)) { frequencyMap.put(word, 0L); } Long oldCount = frequencyMap.get(word); frequencyMap.put(word, oldCount + 1); } return frequencyMap; } static Map countFrequencyInFunctionalWay(List words) { Map frequencyMap = new HashMap<>(); for (String word : words) { frequencyMap.merge(word, 1L, (oldValue, value) -> oldValue + value); } return frequencyMap; } static Map countFrequencyInFunctionalWayInShort(List words) { return words.stream() .collect(Collectors.groupingBy( Function.identity(), Collectors.counting())); } public static void main(String[] args) { List words = Arrays.asList( "Hello", "World", "Bangladesh", "Dhaka", "Hello", "Java", "Lambda" ); Map wordFrequency = countFrequencyInImperativeWay(words); System.out.println(wordFrequency); Map wordFrequency2 = countFrequencyInFunctionalWay(words); System.out.println(wordFrequency2); Map wordFrequency3 = countFrequencyInFunctionalWayInShort(words); System.out.println(wordFrequency3); } }

WordFrequencyCounterInImperativeAndFunctionalWay