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Thank you for all your replies, I have made one of the stupidest mistake of my life, it was just a problem with a name, GreenFoot didn't recognize "Explosion.png" because the file's name was " Explode.png" hahaha !

I think that is because you have information tags in your sound file. Try resaving the files without them.

This looks like a partial stack trace. The first part (including the exception type) has been cut off. Are you able to get the full stack trace? (Try turning on the "unlimited buffering" optional from the terminal menu). Also, what version of Greenfoot are you using?

All your methods called from the act method, except for the 'move' method, could potentially remove the actor from the world. If any but the last one does, you will get that error. You could either place the following line between each method: <Code Omitted>or you can preceed each method call like this example <Code Omitted>

In Level1 act method, add this line: <Code Omitted>

I suggest you create a new simple scenario that reproduces this error, then comment out the adding of the object into the world and upload the scenario, publishing source, here so we can look at the issue first-hand.

@valdes, I am so sorry. I stated that the change in line five was to prevent flicker -- and that is not what I meant to say (that is why the changes was not perceptible to your eye). That change was introduced so that the image of the actor was not continuously being set when it was not changing.

To be specific, the Actor class API says this: 'protected' means you can only call the method from an Actor subclass (or the Actor class which you cannot edit); 'java.util.List' means it returns a List object (btw, the method never returns 'null'); 'getObjectsInRange' is the name of the method; 'int radius' is the first parameter which should be a positive integer indicating how far the search extends; 'java.lang.Class cls' is the seco

You could use a for-loop for that, instead of writing it all out in separate lines. And please, use the code tags next time instead of bold tags.

No. Those statements declare the variables, but do not initialise them (give them a value). So, they get the default value for reference variables, which is null (essentially meaning "no object"). That is why you later get an exception - you're trying to call setLocation on no object. It is difficult to help you because it's not clear what class the "respawn" and "respawnLocation" methods are in. If it is in the Virus class, you don't need to call setLocation on another object. If its in some other class,

Appreciate for the reply but i finally found a scenario that suits my scenario.

Check out my Glutton Babies . Class Comida and subclasses are the falling down objects int the act() method of my World is the random creation

Thank you! I was looking for an explanation on the internet. All of them were very long and complicated and