The Daily WTF: Curious Perversions in Information Technology

2025-08-04 Reply Admin

Adding a null object and "something" with the + operator will give the string "nullsomething". So it is a null protection. Stupid and ridiculous but it works more ore less. Assuming databaseId never is the string "null" od course. But people using such techniques are very likely to introduce value "null" (the four letter string) in their database also.

2025-08-04 Reply Admin

What xorium said seemed wrong, but indeed, that's what it does:

    public class Main {
            public static void main(String[] args) {
                    System.out.println(null + "");
            }
    }

javac Main.java && java Main:

null

warmachine · 2025-08-04 Reply Edit Admin

Actual Java programmers use the StringUtils library from Apache Commons Lang for null safe string comparison.

WTFGuy · 2025-08-04 Reply Edit Admin

Of course the null value is supposed to fail comparison to anything, including another example of the null value. By them pulling the [convert null to "null"] trick, now the comparison succeeds if both parameter values are the null value.

jeremypnet · 2025-08-04 Reply Edit Admin

Of course the null value is supposed to fail comparison to anything, including another example of the null value

Yes in SQL, but this is Java. I've never heard of any semantics like that in Java. In fact null == null has always been true.

Remy Porter · 2025-08-04 Reply Edit Admin

Hunh. I tried basically the same program in an online compiler when writing the article, and it threw an exception, because I wasn't sure what the behavior would be. I'm wondering if there's a version/flags element that makes it behave differently? That doesn't seem very Java.

2025-08-04 Reply Admin

I tried basically the same program in an online compiler when writing the article, and it threw an exception

Then that online compiler has a bug because null + "" gives you "null" since Java 1.0.

Balor64 · 2025-08-04 Reply Edit Admin

The proper way to do this (without third party libraries) would be return Objects.equals(requestedAssetId, databaseAssetId);. If both values are null it returns true, if only one of them is null it returns false, and if neither of them are null it compares their contents.

2025-08-04 Reply Admin

With modern Java versions you don't need to compile, you can run "java Main.java". And from Java 25 on (coming in September) the file can also be simplified:

void main() {
    IO.println(null + "");
}

2025-08-04 Reply Admin

Swing and a miss, Remy and/or whoever submitted this code. There's no WTF here. Concatenating an empty string just helps with null handling. Yes, there's other ways this could've been done probably. But I'm certain this function was implemented as a bugfix for something at some point, and it helps fulfill some design requirements and/or deeply baked assumptions elsewhere in the code. It's not clean, it's not pretty, it's not best practices, but it works. I'm sure of it. And it's not atrocious, so it gets a pass from me.

PS: no, you can't just do Objects.equals(id1, id2). That would change the outcome between a null string and the string "null". It's a dubious way to do things, but changing it would surely break something somewhere, and fully "fixing" it would require a lot of unnecessary work and introduce unnecessary risk.

jeremypnet · 2025-08-04 Reply Edit Admin

I think the "correct" implementation would be

requestedAssetId != null && requestedAssetId.equals(databaseAssetId);

This IMO is clearer than the submitted code, which, as exemplified by the fact that it was submitted and misunderstood even by an online compiler and the site owner, is a little bit obscure.

Ironically in view of my previous comment, it implements SQL null semantics. If you want to return true if both arguments are null Objects.equals() is fine because the fact that the method returns true if one argument is null and the other is "null" is surely an unintended side effect.

Addendum 2025-08-04 13:24: s/side effect/consequence/

Concatenated Validation

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