SLAPP 2 basicObjectProgrammingBug.txt

                FROM PLAIN PROGRAMMIN TO BASIC OBJECT PROGRAMMING


This is an object-oriented version of the simple bug program.

The code for the "bug" has been encapsulated in an "object".

We have a new code to "create" a bug, to set its internal
state, and to tell it to execute  - to "do its thing" over
and over again. We communicate with the "bug" by sending
it "messages", using the following syntax.

		aBug.randomWalk()

is a command to send the object "aBug" the message:

     `set your X and Y coords to xPos and yPos'

The instruction 

		aBug = Bug(1, 40, 40) 

is asking the Bug "Class" to give us an instance of a Bug, 
which we thereafter refer to as "aBug". 

The message aBug.randomWalk() is asking the object "aBug"
to perform it's major action, taking a random walk - but the 
code for doing so is hidden from us here. We just ask it to 
"do its thing", and it does it, whatever it is.

In this case, the "bug" object has four internal variables: xPos,
yPos, worldXSize, and worldYSize.