How to Start Coding a Class -

Required Class Header

This is the required class header.

The class must be public.

class Rectangle

Required Constructor Headers

Three constructors must be coded with the specified constructor headers.

The constructors are static factory methods

The constructors must be public.

//Returns new Rectangle with width and height set to zero.
static newRectangle()

//Returns new Rectangle that is a square with width and height both
//set to method param "aSide"
static fromSide(aSide)

//Returns new Rectangle with width and height set to passed method params
static fromWidthHeight(aWidth, aHeight)

Object Diagram

The object design provides us with a wonderful object diagram.

The object diagram is like gold to a coder because it is so helpful to code the object structure.

Rectangle
  |
  +------- width ------- an integer
  |
  +------- height -- an integer

Using the provided design, we code a simple class shell, to initiate our coding.

class Rectangle {


}

Using the provided object diagram, we code ivar declarations or a code comment about the ivars.

Some coding languages (e.g., Java) will require declaration of instance variables (ivars), while other languages (e.g., JavaScript) will not.

class Rectangle {
	/*
	width - the width dimension of a rectangle (an integer)
	height - the height dimension of a rectangle (an integer)
	*/
}

Constructor Starts

We start off coding the constructors by simply copying in the required constructor headers and adding empty method bodies and "//TODO" tags.

//Returns new Rectangle with width and height set to zero.

static newRectangle() {
	//TODO
}

//Returns new Rectangle that is a square with width and height both
//set to method param "aSide"
static fromSide(aSide) {
	//TODO
}

//Returns new Rectangle with width and height set to passed method params
static fromWidthHeight(aWidth, aHeight) {
	//TODO
}

Constructor Code

Here is the constructor code. Note that we take advantage of code reuse by simply calling another constructor when possible.

Note that we add a "classic constructor". We will typically do this, and call it from the static factory constructor, so that we can code on the instance side with "this" in context.

The classic constructor method header(s) vary per the language, e.g., in Java it would look like

public Rectangle(aWidth, aHeight)

//Returns new Rectangle with width and height set to zero.
static newRectangle() {
	return Rectangle.fromWidthHeight(0, 0);
}

//Returns new Rectangle that is a square with width and height both
//set to method param "aSide"
static fromSide(aSide) {
	return Rectangle.fromWidthHeight(aSide, aSide);
}

//Returns new Rectangle with width and height set to passed method params
static fromWidthHeight(aWidth, aHeight) {
	return new Rectangle(aWidth, aHeight);
}

//--------------------------------------------------------------
//Private (Classic) Constructors

//Classic constructor that accepts width and height params
constructor(aWidth, aHeight) {
	this.width = aWidth;
	this.height = aHeight;
}