Chapter 5 Notes

Site hosted by Angelfire.com: Build your free website today!

Class - a blueprint for an object

Each object has data values and actions associated with it
- data values are private instance variables
- - only available inside te class(scope)
- - every instance of an object is assigned a complete set of unique private instance variables

When an object is instantiated, memory allocations for all private instance variables are issued

Methods are task-oriented events that can be activated through the object

Two types of methods:

void	value-returning
does not return a value	returns a value

Characteristics of an Object:

behavior	state	identity
actions taht an object can perform	values stored by an object	uniquememory allocations for each object
defined by the methods	defined by the private instance variables	created when the objectis instantiated(-new line)

Client & Server interactions

- client sends messages to the server, to invoke the methods
- server performs and reacts according to the client's request(or message)

Object

- an entity that can be manipulated by invoking methods
- like "black box" witha a public interface (methods you call) and hidden implementation (the code and data neded to make the methods work)
- encapsulation - process of hiding implementation details
- object variable: to remember an object you store its memory location in an object variable--container that stores the location of an object
- memory is referenced by pointers
- object variable refers to object, does not contain object

Parameters

- two types of parameters
- - actual - insterted values
- - formal - description of the type of value to be inserted

- both parameters must match in . . .
- - type
- - quantity
- - position

Rectangle class is a class from Java library files
java.out.Rectangle("Abstract Windowing ToolKit")
- each rectangle is defined by the coordinates of the upper-lefthand corner, its width, its height
1 - DECLARE - Rectangle cerealBox; //declares an object variable of type Rectangle
2 - CREATE - cerealBox=new Rectangle(5,10,20,30);
3- PRINT - System.out.println(cerealBox); //same as cerealBox.toString
*/ OUTPUT
java.awt.Rectangle[x=5,y=10,width=20, height=30]
*/

System.out.println(new Rectangle(10,12,50,40);
- this will display teh state of the newly created object, but not store its location in a n object variable.

System.out.println("Jeff".length());
- a string is an object, so the methods can be invoked

4 - Rectangle r;
5 - r=cerealBox
- assign the same reference and is now locating at the same object
6 - r.translate(50,100);
7 - System.out.println(cerealBox);

Constructor

- contain teh instructions on initializing an object
- constructor name is the same as the class name
- only called when teh object is created

Overloading

- methods with teh same name but different parameter list
- compiler decides which constructor to use based on parameter type, quantity and arrangement

Designing a class

1- understand how objects need to behave
2- list method names
3- determine parameters and return type
4- create all constructors
5- implement all methods

Commenting a Class

- standard form of documentation
API(application programing interface)
1- comments start with: /**
2- describe the method's purpose in one sentence. start w/capital lettter and end w/ period
3- for each methoed parameter: @param paramterName short description
4- for every return statement: @retun description of returning value

Iplimenting a class

Order:
- 1 constructors
- 2 methods
- 3 instance fields

Implicit Parameter: this - represents the calling object
Ex. this.radius or this.getArea()

Calling One Constructor from Another
Ex. this("No Name",0.0);

~~~~Home~~~~