Authors: Michael Kölling and David J. Barnes
This project is part of the material for the book
Objects First with Java - A Practical Introduction using BlueJ
David J. Barnes and Michael Kolling
Pearson Education, 2002
It is discussed in chapter 1.
This is a very simple project to demonstrate some characteristics of
You can create various shapes, and you will see, if you do, that those
shapes are drawn on screen (in a window that we call the "canvas").
You can then manipulate these objects: change their position, size and
colour. Try it out: create a few different squares, triangles and circles.
This project is designed as a first example of object-oriented programming.
It illustrates a number of concepts:
- a Java project (application) is a collection of classes
- objects can be created from classes
- from any one class, many objects may be created
- objects have operations (methods)
- operations can have parameters
- parameters have types (at least String and int)
- objects hold data (fields)
- the operations and fields are common to all objects
- the values stored in the fields can be different for each object
The project also demonstrates
- BlueJ object creation
- interactive method invocation
- parameter passing
A good second project to look at after this is "picture", which adds a class
to those ones in this project. That class (named "Picture") uses the shapes
to draw a picture. It can be used to experiment with coding.
Michael Kölling, July 2000