Demo different approaches to get count of duplicated elements in an arrayList

DuplicatesCounter.java

// src: https://github.com/eugenp/tutorials/blob/85922e3a35f492cd8a6faba254f150ef98f7a588/core-java-modules/core-java-collections-list-3/src/main/java/com/baeldung/list/duplicatescounter/DuplicatesCounter.java
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;

/**
 * Demo different approaches to get count of duplicated elements in an
 * arrayList
 */
public class DuplicatesCounter {

    public static <T> Map<T, Long> countByClassicalLoop(List<T> inputList) {
        Map<T, Long> resultMap = new HashMap<>();
        for (T element : inputList) {
            if (resultMap.containsKey(element)) {
                resultMap.put(element, resultMap.get(element) + 1L);
            } else {
                resultMap.put(element, 1L);
            }
        }
        return resultMap;
    }

    public static <T> Map<T, Long> countByForEachLoopWithGetOrDefault(List<T> inputList) {
        Map<T, Long> resultMap = new HashMap<>();
        inputList.forEach(e -> resultMap.put(e, resultMap.getOrDefault(e, 0L) + 1L));
        return resultMap;
    }

    public static <T> Map<T, Long> countByForEachLoopWithMapCompute(List<T> inputList) {
        Map<T, Long> resultMap = new HashMap<>();
        inputList.forEach(e -> resultMap.compute(e, (k, v) -> v == null ? 1L : v + 1L));
        return resultMap;
    }

    public static <T> Map<T, Long> countByForEachLoopWithMapMerge(List<T> inputList) {
        Map<T, Long> resultMap = new HashMap<>();
        inputList.forEach(e -> resultMap.merge(e, 1L, Long::sum));
        return resultMap;
    }

    public static <T> Map<T, Long> countByStreamToMap(List<T> inputList) {
        return inputList.stream().collect(Collectors.toMap(Function.identity(), v -> 1L, Long::sum));
    }

    public static <T> Map<T, Long> countByStreamGroupBy(List<T> inputList) {
        return inputList.stream().collect(Collectors.groupingBy(k -> k, Collectors.counting()));
    }
}