Prelim 3 Topics
CS100
Fall 2000

Overall Prelim 3
+ 100% Java
+ closed book
+ about 4 problems
+ short answer, fill-in-the blank, fill-in-the box

Language Elements
+ keywords
+ primitive types (int, double)
+ identifiers (rules, naming convention)
+ Issues:
  - Java is OOP
  - Java is strongly typed
  - Everything is an object

Flow Control
+ block statements
+ condition: $if$, $if$-$else$, $if$-$else if$-$else$
+ repetition: $while$,$for$,$do$-$while$

Methods
+ syntax
+ components of a header
  - return type
  - name
  - formal parameters (must have types)
+ how to access (from an object or within an object)
+ returning values
  - return value has a type
  - $void$ does not return a value
    but you may still use $return$ w/o a value
+ returning a value and printing are DIFFERENT!
+ all variables pass by value, including references
+ local variables and scope
+ overloading

Classes
+ class is blueprint; object is instance of class
+ INSTANTIATION: creating an object using the class
+ structure of class
  - instance variable(s) (usually private)
  - constructor(s)
  - method(s)
    - setters (set instance vars -> make public)
    - getters (get instance vars -> make public
    - utility (methods used only in class)
+ $this$ uses:
  - this.varname when a method has a local variable with same name as varname
  - refers to current object
  - may also use as a constructor (not required for exam)
+ methods inside a class can all "see" eachother
+ instance vars inside a class can all "see" eachother
+ $toString()$
  - builtin method to print a description of an object
  - activates when code "prints the object"
  - user must define in class to make "pretty" output for "printing the object"

Objects
+ create with $new$ operator:
  1) new Classname(arguments);
  2) Classname refvar; refvar = new Classname(arguments);
  3) Classname refvar = new Classname(arguments);
+ the code $new Classname(arguments)$ returns a REFERENCE to a newly created object
+ a reference is an address of a newly created object
+ alias: setting a refvar to another refvar -- they both point to the
  same object
+ passing the reference to a method means passing the address of an
  object to a local variable -- the local variable becomes as alias of
  the object
+ objects that have no reference variable connection become "unreachable"

Constructors
+ use rules for methods
  but, no return type and have same name as class!
+ may be overloaded
+ if you do not provide a constructor, Java gives you empty constructor by default
+ if you give at least one, Java does NOT automatically give you a default constructor

$static$
+ CLASS VARIABLES: variables in class that are labeled as static
+ CLASS METHODS:   methods in class that are labeled as static
+ all objects in class can see the same static things
+ changing a static variable changes that var's value for all objects in the same class
+ when to use? when all objects in the class need/use the same thing

encapsulation
+ "spread out" code
+ make methods for getting and setting instance variables
+ hide information with $private$ when possible
+ objects "passed inside" another class can directly access members even if 
  the fields are labelled as $private$

$final$
+ modifier for variable to make it constant (unassignable)
+ write constants in all UPPERCASE

strings
+ Strings are objects
+ use string1.equals(string2) to compare equality of string1 and string2

Box Diagrams
+ see online file for entire set of rules