Checking for Collisions in Greenfoot

1. Checking for Collisionsin Greenfoot

2. Greenfoot provides a two important methods that allow an object to detect whether it is intersecting with another object: • atWorldEdge( ) • This method returns a “true” value if an object is at the edge of the world • This method is in the “Mover” class • getOneIntersectingObject(CLASS) • This method returns the object that is being intersected.

3. To make an object disappear if it is at the edge of the world… • Type the following in the class’ act( ) method: if (atWorldEdge() == true) { getWorld().removeObject(this); } -removeObject(this) will remove your object. -atWorldEdge( ) will return a boolean value

4. To detect if an object is touching another object you will use the following method: This will method will return the object that is being touched. getOneIntersectingObject(CLASS); This is class of the objects for which you are looking.

5. Here is an example of how you would use that method: public void act() { checkKeys(); checkCollision(); } public void checkCollision() { Actor collided; collided = getOneIntersectingObject(UFO.class); if (collided != null) { //This will remove the object getWorld().removeObject(collided); } }

6. “collided” is a variable of the type Actor. It will store an Actor object. This method says, “Am I touching a UFO object?” If it is, put that UFO object in the variable “collided.” public void checkCollision() { Actor collided; collided = getOneIntersectingObject(UFO.class); if (collided != null) { //This will remove the object getWorld().removeObject(collided); } } This method removes the “collided” object from the world. If “collided” has an object in it, then do the following…