LECTURE NOTES
SEPTEMBER 29 2004

ANNOUNCEMENTS
First Midterm Exam
  Tuesday October 5 5:00-7:00 pm
  1227 Engr Hall
  Different proctor
  Bring several #2 pencils and your UW student ID

ASSIGNMENTS
10/1 Assignment 1
     CodeLab 4
10/6 CodeLab 5

VARIABLE SCOPE: USING ARGUMENTS, PARAMETERS, AND LOCAL VARIABLES, CONT'D

Why?
- directly using parameter to initialize class variable
What?
- scope
  - where a variable is valid
  - may reuse identifiers among different scopes

Why?
- same identifier refers to multiple variables from different scopes
What?
- resolving names
How?
- first assumes identifier belongs to the most local (method) scope
- if no local declaration or parameter with that identifier, assume class scope
- if no class declaration with that identifier, compiler error

Why?
- also have a local variable or parameter by the same name
- not required otherwise
What?
- specifying a class identifier
How?
  this.<identifier>
- common practice not to use unless necessary

COMMON WAYS TO USE METHODS IN CLASS DEFINITIONS

Why?
- properties are internal details that shouldn't be visible to clients
What?
- methods to get and set data members
How?
- *mutator*
- *accessor*

What?
- calling a method within a method declaration
How?
- name directly
- in conjunction with dot notation

What?
- calling a method within a constructor
How?
- call to another constructor must be the first line
- cannot call instance methods before a call to a constructor

What?
- *overloaded method*
Why?
- avoids duplication
- can implement two similar methods by having one call another
How?
- follow same rules as with constructors

What?
- method that calls private methods in a particular sequence
Why?
- not robust to rely on the client to do so

USING INSTANTIABLE CLASSES

What?
- define a new class
When?
- encounter common task repeated over and over
- avoids cutting and pasting

What?
- using classes together
Why?
- sometimes need more than one class in a program
How?
- reusable *service provider* classes
- nonreusable *controller* class

What?
- developing classes together
How?
- *top-down development*
  - dummy service objects
- *botton-up development*
  - dummy main class

Why?
- implement dummies in either development strategy
What?
- *stub method*

Why?
- never have variations with different data members
What?
- noninstantiable classes
How?
- not covered yet
- OK to implement as an instantiable class

ORGANIZING CLASSES INTO PACKAGES

What?
- using other classes without defining a package
How?
- place class definitions in the same folder

Why?
- more convenient
What?
- using classes in different folders
How?
- create a package and use the import statement

What?
- setting up a package for reuse
How?
- define the package in the first statement of the source file
    package <package name>;
- declare class with the visibility modifier public
    public class <class name> {
    ...
    }
- create a folder with the same name as the package (Java requires a one-to-one correspondence between packages and folders)
- place the modified class into this folder and compile
- modify the CLASSPATH environment variable to include this folder