CSC152 2005S, Class 11: Object Basics, Continued

Admin:
* No reading for Friday!
* More lecture!
* Code online.

Overview:
* Questions and answers
* Writing constructors
* Testing our Fraction class
* Three kinds of classes
* Standard object methods

Questions:
* What is a field, how does it relate to a variable?
  * Fields are very much like variables in that they have types and store values
  * Variables tend to live only as long as the method that contains them.
  * Fields live "longer" - As long as the object that contains them
  * We use them more-or-less the same way within a method
  * To help us remember that we're referring to a field (part of an object) rather than a variable or parameter (part of a method), we use
    objectName.fieldName
    * When a method is to use "the current object", we use "this" as the object name.
* What are we going to return from add?
  * A Fraction!

/Writing constructors/

* Reminder: Constructors are methods that build objects
* In Java, there is a particular syntax that distinguishes "basic" constructor from other methods
  * These construtors are associated with the "new" keyword
* Form: Combine the type and the name into "The name of the class"
	PROTECTION NameOfClass(parameters)
	{
		BODY;
	}
* Example:
	public Fraction(BigInteger _num, BigInteger _denom)
	{
	} //
Morals:
* toString() methods are your friends
* We tend to create a lot of objects
* You can often skip the "toString" when you want to convert an object to a string and Java will "figure it out"

Short "documentation reading" problem.

Friday: Lots of cool additional methods (including testing)

Observation:
* We've seen three "kinds" of classes
  * "Mold" classes provide templaets for building objects (e.g., Fractions)
  * "Main" classes: Provide a main method which builds objects and tells 'em to do things
  * "Helper" classes: Provide methods that do things to other objects  Integer.toString(5);