CPSC 2150 - DAY 5
SEPTEMBER 1, 2016

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Black Box Testing
-----------------

When test plans are based entirely on contracts
Don't change if implementation code changes

White box testing
-----------------
when you look at the code as well as the contract.  

Tracing and Debugging
	.Objective - Locate errors using test inputs

	.Approach - analyze the code on sample test cases

	.Tracing - analyze, but do not execute code
	
	.debugging - execute code

Objects and classes
-------------------

one general principle: information hiding AKA encapsulation

To keep related data and operations together so they stay in "sync"
	.Modifying some part of data, without corresponding changing others
	might make it nonsensical

Date class example:

	.One possible Date class representation
		.int day
		.int month
		.int year
	
	.Representation invariant for valid Date
		.day, month and year should be in sync

	.If day, month, and year can be modified arbitrarily, invalid dates
	could be represented


Through public methods provided by a class, access to the private representation
can be controlled

Date class methods either may not let you set the day, month and year independ.

Object-Oriented Programming
---------------------------

Fundamental component is an object
	.A running program is a collection of objects
An object encapsulates:
	.State(ie data)
	.Behavior(how state changes)

Each object is an instance of a class
	.Class declaration is a blueprint of a class

Declare one class per file

Give file the same name as the class declaration it contains

class Pencil
{
	boolean hasEraser;
	String color = "red";
	int length;
	
	int sharpen (int amount) { .. }

	String getDescription() { .. }
}

note that the invariant is a logical comment.  Here, haseraser is true iff
length >=10.

Members
-------

Two kinds of members in a class declaration

Explicit object creation with new();

Unlike C/C++, memory is not explicitly freed
	.References just go out of scope

	.Automatic garbage collection (eventually) deletes unreachable objects

Initialization of an Object's Fields

	.Implicit: Default initial values based on type
	.Explicit: initialization with field declaration

	.Special method: constructior

		.Syntax: name is same as class, no return type.

	
Visibility
----------

private
public


Group member declarations by visibility

No fields should be public
Don't provide public accessor methods for getting and setting private fields
	.there's no point in making them private in the first place!


Constructior arguments that are used directly to set object fields can be
 given the same name as the field.

Method Overloading

	.A class can have more than one menthod with the same name as long
	as they have different paramenter lists

The compiler knows which method to used bsed on the type of parameter passed
Differing only return type is NOT allowed!