A small piece of code which is going to inspire you to try out Kotlin

#kotlin #java

A few months ago I’ve started to discover Jetbrains’ Kotlin language which gave a good impression to me. I can't express my thoughts better than this comment

Kotlin isn’t revolutionary but that’s what is nice about it. If you want revolution then there is Scala and all its headaches. If you want a language that basically codifies Effective Java then that’s Kotlin. — meddlepal@reddit

There is a bunch of excellent tutorial on the web, and I don’t want to bore you with the basics, I just simply want to show you through an example that besides the highlighted sentence Kotlin is less verbose than Java.

So given a string as key, and a list of integers as value. Add a value to the key's list if its exits, otherwise create the list first, then add the value for it.
Java version

Kotlin version

So don't hesitate it absolutely worth a try :)

Oldest comments (11)

Evan Oman • Dec 8 '17 • Edited

I love just about everything I have seen from Kotlin, but the snippet you added can be closely replicated in Java 8:

public static void main(String[] args)
{
    /* Init Map */
    Map<String, List<Integer>> myMap = new HashMap<>();
    List<Integer> l = new ArrayList<>();
    l.add(32);
    myMap.put("aaa", l);

    /* New kv pair */
    String key = "aaa";
    Integer value = 2;

    /* Add the new value */
    myMap.computeIfAbsent(key, k -> new ArrayList<>())
            .add(value);
}

Zoltan Polgar • Dec 8 '17

Hi Evan, thank you for this snippet! I wasn't familiar with computeIfAbsent method. :)

Evan Oman • Dec 8 '17

No problem! It is amusing watching Java add a lot of these kinds of features from Scala and Kotlin.

(((Florian Schätz))) • Dec 12 '17

Java 9 will also have some nice factory methods, so you will probably be able to write something like...

Map map = Map.of("aaa", List.of(32) );

Nurettin Onur TUĞCU • Oct 13 '18 • Edited

Actually, the java example is better, since the lambda is lazily evaluated. putIfAbsent will always try to construct it's second argument even if it isn't in the map. However, that doesn't mean you can't use it in kotlin as well.

Łukasz Wiktor • Dec 12 '17 • Edited

I see 2 identical code snippets...

Łukasz Wiktor • Dec 12 '17

Ok, I see it's been fixed.

Jan Galinski • Dec 13 '17

Not for me, I still see the Lazymap.java twice

Łukasz Wiktor • Dec 14 '17

It may be something wrong with the dev.to platform. Looks like it's serving previous versions of the post occasionally. Sometimes I'm getting this post loaded without the second snippet at all.

Adrian B.G. • Dec 12 '17

I don't think that this is a good example, this hacker type/python style code is not good for anyone, is hard to understand, maintain, extend, catch errors and so on. The first snippet can be understood by most engineers that worked in any C like language, the 2nd ...probably under 10%.

I'm more interested when Kotlin will be able to build iOS apps, then it will be on my radar (shooting 2 platforms with 1 language).