How to Start Coding a Class -

Required Class Header

This is the required class header.

The class must be public.

class DynamicArray

Required Constructor Header

A constructor must be coded with the specified constructor header.

The constructor is a static factory method

The constructor must be public.

//Returns a new empty DynamicArray
//with defaults initCapacity=10 and growthFactor=2
static newEmpty()

//Returns a new empty DynamicArray using passed parameters
static fromCapacityGrowthFactor(anInitialCapacity, aGrowthFactor)

Object Diagram

The object design provides us with an object diagram.

Note the underscore in "_size" (to avoid name collision with method "size")

Note that the "fixedArray" ivar will contain elements plus "blank slots" (nulls).

DynamicArray
  |
  +------- fixedArray ------- a fixed array
  |
  +------- growthFactor -- a floating point number
  |
  +------- _size -- an integer
  |
  +------- initialCapacity -- an integer

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 DynamicArray {
	/*
	fixedArray - a fixed array
	growthFactor - a floating point number
	size - an integer
	initialCapacity - an integer
	*/
}

Constructor Starts

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

//Returns a new empty DynamicArray
static newEmpty() {
	//TODO
}

static fromCapacityGrowthFactor(anInitCapacity, aGrowthFactor) {
	//TODO
}

Constructor Code

Below is the constructor code. We have also added a "classic constructor" and helper methods to make our code simple.

The classic constructor method headers vary per the language. See "Java Note - Classic Constructor" below.

//--------------------------------------------------------------
//Public Constructors

//Returns a new empty DynamicArray
//with defaults initCapacity=10 and growthFactor=2
static newEmpty() {
	//Use defaults
	return new DynamicArray(10, 2);
}

static fromCapacityGrowthFactor(anInitialCapacity, aGrowthFactor) {
	return new DynamicArray(anInitialCapacity, aGrowthFactor);
}

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

constructor(anInitialCapacity, aGrowthFactor) {
	this.initialCapacity = anInitialCapacity;
	this.growthFactor = aGrowthFactor;
	this.reset();
}

//--------------------------------------------------------------
//Helpers
reset() {
	this._size = 0;
	this.fixedArray = this.newFixedArray(this.initialCapacity);
}

newFixedArray(aSize) {
	//Varies per coding language (see next section for examples)
	//Construct fixed array with null elements, and with size "aSize"
	//Null elements are "blank" spots where "actual" elements will be placed
	//TODO
}

Java Note - Private (Classic) Constructors

Here is the classic constructor header in Java.

private DynamicArray(int initCapacity, double aGrowthFactor)

JavaScript Note - newFixedArray

This is how we could construct a fixed array in JavaScript.

newFixedArray(aSize) {
	//Construct fixed array with null elements, and with size "aSize"
	//Null elements are "blank" (available) spots where "real" elements will be placed
	let fixedArray = Array(aSize);
	// Fill with nulls
	fixedArray.fill(null);
	// Assure it is fixed
	Object.seal(fixedArray);
	return fixedArray;
}

Java Note - newFixedArray

This is how we could construct a fixed array in Java.

@SuppressWarnings("unchecked")
private E[] newFixedArray(int aSize) {
	return (E[]) new Object[aSize];
}