Overview

• Preliminaries.
  • Admin.
  • Questions.
• Writing fields.
• Writing constructors.
• Writing methods
• Standard methods.
• Lab!

Preliminaries

Admin

• Apologies if I'm discombobulated - I had code problems in 151 and 207 today.
• You should have received current grades from me. Let me know if you have questions.
• Extra credit:
  • Convo Feb. 5 at noon in JRC 101: Pussy Riot and Putin.
  • Wednesday Extra, February 5 at 4:30 in 3821, AppDev
  • CS Table Friday: NP Completeness.
  • More?
• New lab partners
• Mentor session tonight at 7:00 in 3821.
• Lots of people absent. They should be sending me email to explain why.

Upcoming Work

• Reading: Debugging
• Homework 3, Due Wednesday
• Today's writeup: Exercises 2 and 4
  • Due Wednesday.
  • Subject: CSC 207 Writeup 7: Classes (YOUR NAME(S))

Questions on the homework

Writing classes

• A class is a template for making objects
• It includes methods
• It includes fields - the data
• It includes constructors - how to build new objects
• Each of these have a protection level
  • public - anyone
  • protected - class, package, subclass
  • nothing (package) - class and package
  • private - only this class

• In Java, we also have

  • static fields - shared by all objects
  • static methods - can be used without objects
  • constants

  • Writing fields

• A lot like variable declarations

  TYPE NAME;

• Convention: name starts with lowercase letter and uses camelCase

• Can have a protection level. - Usually package or private.
• Becomes usable in every object in the class - individual
• Tend to refer to them internally as
  • this.fieldName (in the current object)
  • other.fieldName (in another object)

• You can drop the this. and it is assumed. But it's ambiguous

  public class Amby { int x;

  public int multiplyBy(int x) { return this.x*x; } } // class Amby

Writing methods

• A lot like C

  RETURNTYPE NAME(PARAMS-WITH-TYPES) { CODE }

• Optional protection level
  • Sam's custom: Separate public and non-public methods in your class
• camelCase again
• Can refer to fields

Writing constructors

• Look a whole lot like methods
• Name must match the name of the class.
• No return type

• No return call

  ClassName(PARAMS) { } // ClassName(Params)

Standard methods

• toString()
• equals()
• hashCode() - a number that represents the object
• compareTo()

Lab

We'll talk about exceptions on Wednesday.

Why doesn't Sam like

public Fraction multiply(Fraction multiplicand)
{
  int productNum = this.num * multiplicand.num;
  int productDenom = this.denom * multiplicand.denom;
  ...
} // multiply