Stream testing

TestStream

package com.alamer;

import lombok.AllArgsConstructor;
import lombok.Data;

import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;

public class TestStream {
    public static void main(String[] args) {

        User u1=new User("u1");
        User u2=new User("u2");

        Nazn n1=new Nazn(1,u1);
        Nazn n2=new Nazn(2,u1);
        Nazn n3=new Nazn(3,u2);
        Nazn n4=new Nazn(4,u2);
        Nazn n5=new Nazn(5,u1);
        List<Nazn> list= Arrays.asList(n1,n2,n3,n4,n5);

        Map<User, Long> collect = list.stream().filter(nazn -> nazn.getUser() != null).collect(Collectors.groupingBy(Nazn::getUser, Collectors.counting()));


    }


    @Data
    @AllArgsConstructor
    private static class Nazn {
        int id;
        User user;
    }


    @Data
    @AllArgsConstructor
    private static class User {
        String userName;
    }


}