Yes, of course! - just see my scenario http://www.greenfoot.org/scenarios/3927 for an example of randomly spawning enemies :) (however mine has a limit of how many enemies can be in the world at any one time - i have it so that if the number of enemies in the world is less than the limit, it spawns a zombie in a random location) You just do something like obviously if you want them spawning in different (random) places, you have to do another getRandomNumber() call for the x, and y co-ordinates - here's an example: By the way, if you're not used to using Greenfoot.getRandomNumber(int limit) you can see here. Basically if you do Greenfoot.getRandomNumber(50), what you're getting is a random number between 0 and 49 inclusive - so my statement means if(a 1 in 50 chance). Also if you want the rate of spawning to increase with time, then you'll want to have 2 fields, like the following: (which means you'd change the statement to and then in the act method of the class in which you have the 2 fields (and, presumably, the statement - so I'm going to assume you're putting this in your world class) you add the following: The reason I added an extra && rate > 2 check is because otherwise eventually the rate would go negative, and you can't do Greenfoot.getRandomNumber(negative number). If I'm not making any sense, give me a heads up about what you're unclear about and I'll go over it again, but better - hopefully this should suffice though. Oh and a final note, you'll want to fiddle with the 100 in timer%100 and the 50 in int rate = 50; to get the spawn rate you're looking for :) Oh and another thing - if you get any errors tell me what they are - I've written this code straight into the text box so I haven't got greenfoot to error-check it

The 'addObject(Actor, int, int)' method is a world class method, and also the x and y need to be integers, so line 49 should beOf course, ZombieWorld should be replaced with the name of your world (unless that IS the name of your world).

Even just: ... should be fine. No need for the cast here.

I did not think it was needed, as the method is an inherited one (just trying to be a little more on the cautious side, as I never had taken any classes that were anywhere near Java-related).

If you wanted them to spawn from any border

Oneshot, you need to think a little bit about what the code is doing rather than just blindly copy-pasting it. The code that danpost gave you adds in a zombie at a random location. If you just paste that into the "act" method, then you'll add another zombie every time that act() is called - that is a pretty high rate. In the code before that, you had an "if" statement to control the rate. So, you need to combine the two parts! (fill in the proper code).

Yes, the way you have it written each zombie will spawn more zombies. If that's not how you want it, you should spawn the zombies from a different class - probably the world. Also, it's not clear what the purpose of lines 27-29 are. Perhaps you are trying to have the bullets "kick" the zombie back, however, you never initialise 'x' and 'y' to anything so they do not represent the zombie's current position and instead they are usually at 0,0 - this is probably why zombies appear to "spawn" in the top left. Perhaps you need to call getX() and getY() in order to get the current zombie position.

You don't need to call getWorld() from the world class, because you are in the world already. So: getWorld().addObject(...) becomes just addObejct(...)