Java map creation

Question

So Im making a topdown 2d rpg in slick2d and lwjgl 2, and I wanna make a map, but not just random map, something like this:

The blue stuff is water and rivers, the gray in the middle is "the mountains" and such. How could I create such a map design, but a random one through code. If anyone has an idea of how this is done, please tell me, or even link a tutorial if you know a good one. Thanks.

Answer 1

The map in your screenshot is from Realm of the Mad God. It was generated from the url that Chris Mills-Price linked to. There's a flash demo on that page, a complete description of the algorithms used, actionscript source code, and links to Java code.