Java 8 - count unique String using Collectors.groupingBy

import java.util.ArrayList;

import java.util.List;

import java.util.Map;

import java.util.function.Function;

import java.util.stream.Collectors;

​

public class CountStrings {

​

    public static void main(String[] args) {

​

        List<String> usernames = new ArrayList<>();

        usernames.add("Kate"); // Kate - 1st time

        usernames.add("John");

        usernames.add("Ann");

        usernames.add("Kate"); // Kate - 2nd time

        usernames.add("Kate"); // Kate - 3rd time

​

        Map<String, Long> usersToCount = usernames.stream().collect(

                Collectors.groupingBy(

                        Function.identity(), Collectors.counting()

                )

        );

​

        usersToCount.forEach(

                (user, count) -> System.out.println(user + ", " + count)

        );

    }

}

Ann, 1

Kate, 3

John, 1