LECTURE NOTES
CHAPTER 2

ASSIGNMENTS
- today
  - exam conflicts/McBurnie
  - survey
- 2/2 CodeLab
- 2/4 Assignment 4

ADMINISTRIVIA
- must start assignments early if want help from consultants
- textbooks should be available next Wednesday
- CodeLab comes bundled w/ book
- lab day Monday
  - CSS 1370
  - must have UW student id # or previous cs id & pwd

2.5 NUMBER TYPES

- every value has a type
- type limits how can use value in program

- distinction between
  - integers
    - whole numbers only
    - int type
  - floating-point (real) numbers: can have fractional parts
- never use commas to type numbers
- double type
  - use for floating point numbers
  - can use scientific notation, e.g. avogadro = 6.022e23
- why integers?
  - take less space
  - faster to process
  - no rounding errors
- operators + - *
  - precedence
  - parenthesis

2.1 VARIABLES

- variable
  - storage location
  - type, name, contents
  - use in place of the object stored
- declaring a variable
  - name something so that you can refer to it later
  - "uninitialized variable error": must declare a variable before you can use 
    it
  - specify type
    - intended use determines
  - specify name
    - describe the purpose of the variable
    - must be an identifier
- identifier: name of a Java something
  - rules
    - letters, digits, underscore
    - cannot start with a digit
    - no reserved words
  - variable conventions
    - begin with a lowercase letter
    - if multiple words, used "mixed case", e.g. bankAccount

2.2 ASSIGNMENT

- assignment operator = 
  - sets the value associated with a variable
  - evaluated from right to left
  - "gets" not "equals"
- type declaration errors
  - literals have implicit types
  - if the type of the value and the variable don't match, compiler error  
- initialization
  - giving a variable its first value
  - error to use a variable before initializing it

2.3 OBJECTS, CLASSES, AND METHODS

- object
  - entity that you can manipulate in your program via methods
  - don't need to know internal organization
  - well-defined behavior
- method
  - sequence of intructions that access internal data
  - to use, must only know purpose, not how done
  - e.g. length
- calling a method
  - telling an object to do something
  - dot syntax
- class
  - defines the characteristics (data) and behavior (methods) of a particular 
    kind of object
  - every object belongs to exactly one
  - public interface: what you can do with the object
  - private implementation: how these actions are carried out
- a variable can have a class as a type
- primitive types vs. classes
  - primitives: double, int
  - primitivies have no methods

2.4 METHOD PARAMETERS AND RETURN VALUES

- parameter
  - input to a method
  - specify in more detail what the method does
  - e.g. PrintStream.println()
  - implicit: the object on which the method is invoked
  - explicit
    - the ones in the parenthesis
    - every method has zero or more
- return value
  - method output that can be used by your program
  - not all methods have it
  - when reading code, think of the return value replacing the method
- method definition
  - occurs in class
  - specifies 
    - type of returned value
    - type and number of explicit parameters
  - implicit parameter: object of the class where the method is defined
- how does the compiler find the code?
  - first, find the class of the implicit parameters
  - then, match the name
- overloaded methods: multiple methods of the same name in the same class
  - number-type of parameters must differ
  - compiler finally looks for match in number and ordered types of parameters

2.6 CONSTRUCTING OBJECTS

- construction
  1. new operator makes an object, given a class name
  2. construction parameters initialize the object's data
  3. object is returned
  - e.g. color(int r, int g, int b) // 0-255
- some classes let objects be constructed in multiple ways: 
  color(int r, int g, int b, int a)

2.7 ACCESSOR AND MUTATOR METHODS

- accessor method
  - returns some info about an obj w/out changing it
  - e.g. color.getRed()
- mutator method
  - changes something about an obj
  - e.g. color.redder(int howMuch) // fictitious

2.8 IMPLEMENTING A TEST PROGRAM

1. Provide a new class
2. Supply a main method
3. Inside the main method, construct one or more objects
4. Apply methods to the objects
5. Display the results of the method calls

- package: collection of related classes
- import statement
  - when using classes defined elsewhere, must tell compiler where to find 
    their code
  - syntax
  - e.g. import java.awt.Rectangle
  - everything in java.lang is imported automatically

2.9 THE API DOCUMENTATION

- javadocs: http://java.sun.com/j2se/1.5.0/docs/api/

2.10 OBJECT REFERENCES

- variable whose type is a class 
  - holds the memory location of the object, not the object 
    itself
  - is called an object reference
  - sharing
- primitives actually contain their values
- example
- to save space, b/c objects can get large
- only significant when multiple variables refer to "same 
  thing"