PattyMelt is an implementation of notch's DCPU-16 in Java.

Once you have it built, you can run something like:

java -cp build/classes com.stackframe.pattymelt.PattyMelt test/hello.bin

or

java -jar pattymelt.jar test/hello.bin

to see a hello world program run on the console.

You can find a binary download and examples at http://mcculley.github.com/PattyMelt/