Review for exam

1
Review for exam 2

• COSC 101

2
Classes VS Objects

• Classes are the blueprints
• Objects are the houses
• Objects are also called instances

3
Instance variables

• Also called instance fields
• Encapsulate the state of an object
• bank accounts balance
• miles on a cars odometer
• etc

4
static variables

• also called static fields
• Only one copy shared everywhere in the program
• Good for constant values
• suit or rank of a card

5
Rules for fields

• All fields in a class are instance
• unless specifically declared static

6
Methods

• You absolutely must know the difference between
  defining a method and using a method

7
3 varieties of methods

• Constructor
• instance methods
• static methods

8
Constructor

• Special instance method that creates a new
  object/instance
• also has a method body that executes after the
  new object is created
• invoked using the Java keyword new

9
instance method

• Can manipulate instance variables
• Must be invoked on an instance
• Can invoke other instance methods inside the same
  class
• Can create instances of other classes using the
  constructor

10
static methods

• stateless
• cannot access instance variables at all
• most useful for functions that compute their
  result only using their parameters
• Math.pow(base, exp)
• Math.max(x, y)

11
Defining methods

• All methods are instance
• unless declared static

12
To define a method

• signature
• visibility
• return type
• method name
• parameters
• Then provide a method body

13
Exceptions

• Constructors NEVER list a return type
• Constructors NEVER return values

14
Invoking constructors

• new Point(6, 19)
• returns a reference to a new instance of a point

15
instance methods

• Must be invoked on an instance
• b1.deposit(65.50)
• pixel.setRed(200)
• point.moveX(10)
• Invoking one instance method from another
  instance method that is defined in the same class
  can be done using this
• this.deposit(50.00)
• or not
• deposit(50.00)

16
invoking static methods

• Invoked on the name of the class
• Math.max(10, x)
• Can be invoked without the classname from inside
  the class where its defined