Overview

• Prelmiinaries.
  • Admin.
  • Questions on HW4.
• More on the text block example.
• Inheritance basics.
• Lab.

Admin

• Warning! It's Friday the 13th (class)
• Reading for Monday: Documentation with Javadoc
  • Ready!
• EC Opportunities
  • CS Extras Thursday @ 4:30: Jennelle Nystrom on Microsoft
  • CS Table Friday (pair programming)
  • CS Table Friday next (The Story of Mel, A Real Programmer)
  • Other?
• If you choose to drink alcohol this weekend, please choose to drink responsibly.
• I'm trying to do very little lecture today. We'll see if I succeed.
  • Minor fail
• Updates
  • Lab continued on Monday
  • Homework due on Tuesday night

HW4

How should we evaluate the following?

    r1 = 2/3
    1 + r1

You should give something like the following

    2/3, 5/3

What would you put in the Fraction class? (We'll do this as a group.)

• Constructors
  • Fraction(int,int)
  • Fraction(int) - N/1
  • Fraction(BigInteger,BigInteger)
  • NOT Fraction(Fraction) - That's just cloning
  • Fraction(BigInteger)
  • Fraction(String) - new Fraction("11/15")
  • Fraction(long,long)
  • Fraction(double)
• Public methods
  • Fraction add(Fraction other)
  • Fraction subtract(Fraction other)
  • Fraction multiply(Fraction other)
  • Fraction divide(Fraction other)
  • Fraction pow(int expt)
  • double doubleValue()
  • BigDouble bigDoubleValue()
  • Fraction reciprocal()
  • Fraction negate()
  • BigInteger numerator()
  • BigInteger denominator()
  • Fraction fractionalPart()
  • BigInteger wholePart()
• Standard methods
  • Fraction clone()
  • String toString()
  • int hashCode()
  • int compareTo(Fraction other)
  • boolean equals(Object other)
• Private methods
  • void simplify()
  • void cleanup()
• Methods that we don't really want to implement and Sam won't expect us to implement
  • Fraction pow(Fraction expt)
  • Fraction sqrt()
  • Fraction log()
  • BigInteger round()
  • BigInteger ceiling()

Hash code implementation

* `int hashCode() { return 1; }`
* `int hashCode() { return numerator.hashCode() * denominator.hashCode(); }`

Why won't my test code work

    public void test() throws Exception {
        ...
    }

More on the text block example

• A line is a text block
• The vertical compositon of two text blocks is a text block
• A textblock that is boxed is a textblock

    +-------+
    | Hello |
    +-------+

• What are the important ideas in this example?
  • Recursive definitions of data types
  • Supported by polymorphism
  • Extensible!

Inheritance basics

• General concept: We can define new classes in terms of old
• Why not have the language do what we would do by hand Foo extends Bar
  • Implicitly copy all of the fields and methods of Bar into Foo
  • Foo can add new methods and fields
  • Foo can replace methods (but not fields)
• Supports polymorphism
• Lets Aristotilian philosophy add to Platonic philosophy

Lab

• Start it in class.
• We'll continue it on Monday. People are having more difficulty than I expected.
• Sorry that I failed in being succinct. I'll try again on Monday.

Sample code

public class Counter {
   int count;
   int start;

   public Counter(int i) {
       this.count = i;
       this.start = i;
   } // Counter(int)

} // class Counter