CSC152 2004F, Class 16: Standard Methods

Admin:
* Labs good?
* Comments on eboards?
* Exam distributed Friday
* Homework grading for Friday (I hope)
* New term: "Mold class" (replaces "Template class")
  * Main class: Provides main method.
  * Mold class: Provides guidelines for building objects.  Contains fields and constructors.
  * Interface: Provides a list of methods, but nothing more.
  * Template class (official): Class that accepts other classes as parameters.
* Problem with switch statements 
  + Moral: If you use a return in a case, you don't need the break.

Overview:
* Why have standard methods?
* The toString method
* The equals method
* The compareTo method
* The clone method
* The hashCode method

/Standard Methods/

* Methods you are likely to put in almost every class that's not a main class.
* Five standards:
  + toString: Represents the object as a string
  + equals: Compare the object to another
  + compareTo: Compare the object to another
  + clone: Make a copy
  + hashCode: Represent the object as an integer
* Why have these standard methods?
  * Why have toString?  
    * Gets called as default.
    * Useful to be able to print objects.
    * If everyone uses the same name, it's easier to write code that uses this method.  (Sounds like an interface issue.)
  * Standard methods mean that others can write general methods that use our objects, even if they don't know about our objects in advance.

/Equals: Compare for Equality/

* Note: Your first task is to determine what "naturally equal" means.
  * E.g., both Polar(2.0, Math.PI/2) and Point(0.0, 2.0) are Vec2Ds
    * No: They are different types
    * Yes: Both represent the point (0,2)
  * E.g., are Point(0.0,2.0) and Point(0.00000001,1.99999998) equal?
    * No: Different values (however, pretty darn close)
    * Yes: If you don't need that many decimal places
    * Yes: Java tends to approximate.
* The signature (form) of the equals method
	public boolean equals(Object other)
* Problem: General Objects don't provide the methods you want
* Solution: Cast those objects to the appropriate type
	NewType newname = (NewType) oldobject
* Problem: If you cast inappropriately, your program crashes
* Solution: Check if you can cast
	if (object instanceof ClassName)

/CompareTo/

* public int compareTo(Object other)
* Return negative number for "I'm less than other"
* Return 0 for "I'm equal to other"
* Return postiive number for "I'm greater than other"
* Probably have to cast as in equals
* If it's not castable, crash and burn

/Clone/

* public Object clone()
* Make a copy.
* Useful for mutable objects.

/HashCode/

	public int hashCode()
* Return some integer.
* Equal objects should return the same integer.
* Unequal objects should be unlikely to return the same integer.

/Homework/

* Implement all of these, except hashCode, for DateV1.

Convo tomorrow in Bucksbaum.  See a Frank Sinatra movie and learn about "whiteness"