CSC 297.Java 2003F, Static vs. Object Methods

Admin:
* Demos of factoring programs
* Assignment: Design a RationalNumber class and suggest what methods should be object methods and what methods class methods

Topics:
* Object model, reviewed
* Object fields, revisited
* Object methods, revisited
* Static methods, revisited
* Static fields
* Choosing a method type

Notes on Alex's code
* Comment procedures and classes (and equally big things) with a block comment of the form
	/**
	 * Yadda yadda yadda.
	 */
* Break up your code with succinct one-line comments that explain each chunk.  These comments should be prefaced by //
* Use indentation to show the logical structure of your code.
* Think about efficiency.
* Close braces belong on lines by themselves or they are easily lost.
* Careful in how you comment close braces.
* Using boolean "sentinels" for loops is often a good idea.


Object model, reviewed
* Object gather data and functions together
* In Java, classes describe the general form of some objects

Object fields, revisited
* The "regular" fields in a class are places in which to store the data for corresponding objects
	double x_coord;
	double y_coord;

Object methods, revisited
* The "regular" methods in a class are things that use or change these values.
	public double distanceFromOrigin()
	{
	  countOfDFOcalls = countOfDFOcalls + 1;  
	  return Math.sqrt(x_coord*x_coord + y_coord*y_coord);
	}
Static methods, revisited
* Sometimes you want to write methods that are not associated with any particular object but with the class as a whole.
  * E.g., convertAStringToaPoint
  * These are called "static" methods
  * Declared with
	PROTECTION static RETURN_TYPE NAME(PARAMS)
	{
	}
  * Static methods cannot reference object fields
  * How many times have I called distanceFromOrigin on *any* point?
  * Probably needs an accompanying "static" field (associated with the class as a whole).
  *
	PROTECTION static TYPE FIELD_NAME = INITIALIZATION;
  * E.g.
	private static int countOfDFOcalls = 0;
  	public static int howManyTimesWasDFOCalled {
	  return countOfDFOcalls;
	}
Choosing a method type