CSC152 2005F, Class 19: Java Interfaces

Admin:
* Donuts!
* Reading for tomorrow: Polymorphism
  * Not quite ready, but soon
* Questions on the exam?
  * polar
  * getTotal()

Overview:
* Summary of reading
* Questions and answers
* Lab

/Exam Questions/

Q: How do I create a Vec2D using Polar coordinates?
	Vec2D p = Vec2D.polar(radius,theta);
Q: When testing, do I need to write testers that interact with the user, or can I hard-code the tests and change as necessary?
A: Do what you want (unless I've told you something explicit).
Q: Shouldn't getTotal() return a double?
A: No.  double are inaccurate.  It makes sense to return the number of cents.
Q: What do you want back?  
A: The number of cents as a long.
   this.quarters*25 + this.dimes*10 + this.nickels*5 + this.pennies;

Side note: Some of you have learned the following EVIL shorthand
	import java.io.*;
Meaning "for an class in the package java.io, if I use the name of the class, assume I mean java.io.NameOfClass"
Problem: Leads to ambiguity for the *reader* of your code
	import java.io.*;
	import java.util.*;
	import rebelsky.cs152.*;
	...

	FizzBuzter fb = new FizzBuzter();

Interfaces
* Good programming strategy: Separate what from how
  * Client programmers should only know the what
  * Helps the person doing the development b/c it can reveal the next step
  * Helps Sam when he's helping you - Distinguishes between goals of code from what someone happened to write
* Supported through interfaces - lists of related methods that we expect certain classes to provide
	public interface INAME
	{
	  METHOD DECLARATIONS W/O BODIES
	}
* We tie the how to the what when imlpementing a class
	public class CNAME
	  implements INAME
	{
	}

/REFLECTION/

* Another reason to separate the what from the how: Choose different implementations
* New form of lab?
* Bug/Feature in computing distance (doesn't "wrap around")
  * Make a new copy of DateHelper.java if you want
* Note: if CNAME implements INAME, you can use an object of type CNAME wherever you expect a value of type INAME