Java Enums with constant-specific methods

One of my colleagues introduced me to this handy language feature of Java 1.5 and I wanted to write an article about it because I hadn't seen this before.

Using google reveals that it is already well documented if you RTFM, but I will repeat it here because talking to other Java developers indicates that it isn't as well known as it deserves to be. Here's a slightly reworded extract from the first hit on google or bing for "java enum":

You can declare abstract methods in an enum and override them with a concrete method in each constant. Such methods are known as constant-specific methods. Here is an example using this technique:

public enum Operation {
  PLUS   { double eval(double x, double y) { return x + y; } },
  MINUS  { double eval(double x, double y) { return x - y; } },
  TIMES  { double eval(double x, double y) { return x * y; } },
  DIVIDE { double eval(double x, double y) { return x / y; } };

  // Do arithmetic op represented by this constant
  abstract double eval(double x, double y);
}

Copyright © 2009 Ivan Moore

New version of Jester released

It's been a while since I last updated Jester (a mutation testing tool).

Today I released a new version of Jester - not much changed - but hopefully a bit easier to get it to work, based on my experiences of trying to use Jester when I haven't tried for a while.

It now doesn't read configuration files from the classpath - instead you specify the relevant files on the command line.

Copyright © 2009 Ivan Moore

XpDay London, 7th & 8th December 2009

It's XpDay soon - book your place now. The Keynotes look particularly good this year.

On Monday there's an experience report that looks very interesting "When Agile Might Not Be The Best Solution" - it's good to see this sort of experience report on the programme because there's probably more to learn from it than one which goes something like "we did XP and it worked".

There are lots of other interesting looking sessions too - plus lots of open space sessions which can be excellent.

Copyright © 2009 Ivan Moore