Category: Programming

Don’t use Set.of().contains(). Use switch instead.

Set.of(a, b, c).contains(value) might seem clever and while it is easy to read it’s way slower than switch(x) {case a,b,c -> true}.

We often have to check if a value is one of a given set of values. But we don’t want to write code like this:

if (value == SomeEnum.FOO || value == SomeEnum.BAR || value == SomeEnum.QUX) { ...

Some use a Set and write it like this:

if (Set.of(SomeEnum.FOO, SomeEnum.BAR, SomeEnum.QUX).contains(value)) { ...

But now the runtime has to create a Set each time this line is run and it also has to call the method contains. And it can’t even handle null. In Java we have a much better alternative: The switch expression. You can use it like so:

switch (value) { case FOO, BAR, QUX -> { ... }; case null, default -> {}; }
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My first inline class for Java

I’ve once made a simple helper class for a set of bytes stored as an integer bitfield. So the idea is that each of the 32bits is used to represent if the ordinal number is in the set or not. This only works for the bytes 0 to 31.
Now this is an “inline class” – something we will get with Project Valhalla.
Here’s the branch of my project:
https://github.com/claudemartin/smallset/tree/valhalla

For this to work you need a JDK with a preview of Project Valhalla. Check java.net for that: http://jdk.java.net/valhalla/

Just download that JDK, clone my branch, build using Ant, and see what you can do with it. It’s actually a good example of an inline class, because it is just an integer (primitive) value but has methods (like a referenced type would). It doesn’t need object identity, but should still behave like an object. For example the sets are comparable. The type actually implements the Comparable interface.

Note that this might not work with newer JDKs. I used JDK 14 + valhalla from java.net and the feature might look quite different in newer releases of Java.

Using WSL from Java

With Windows Subsystem for Linux (WSL) we can now use Linux tools, such as grep, rsync, ssh, and network commands, such as dig and netstat, on Windows directly. No need for cygwin or other 3rd party software.

Here’s an example on how uname is unknown to Windows, but WSL (Ubuntu in my case) knows it:

WSL can be used to run Linux commands, such as uname.
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Misconceptions about Dates and Time

Was 1900 a leap year and does every minute have 60 seconds?

In Java we have a new API for Date and Time since Java SE 8. Before that, there was already an API with mutable dates and fore some reason there was a date just for SQL.
Many were not happy with the old API. There was Joda-Time, which later became the basis for JSR-310 and is now found in the package “java.time”.

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Stalin-Sort

Stalin-Sort using divide and conquer.

I just love this idea:

I came up with a single pass O(n) sort algorithm I call Stalin-Sort. U iterate down the list of elements checking if they are in order. Any element which is out of order is eliminated. At the end u have a sorted list

But when you have an input such as [42,1,2,3,4,5,6] you just get
[42] instead of [1,2,3,4,5,6]. You can get a better result if you use divide and conquer. And that is something Stalin would do, don’t you think? So I implemented a recursive solution in Java. It tries all possible results, which is not a single pass and therefore defeats the purpose of having a fast O(n) algorithm. And my implementation isn’t even in-place. A new data structure has to be created. That’s why I also added an implementation using a linked list, which is what Mathew describes.

The code is on pastebin: https://pastebin.com/rEmvZSiA