Introduction to Classes, Objects, Methods and Strings - Java: How to Program Early Objects - page 70

3.1 Introduction
3.2 Instance Variables, set Methods and
get Methods
3.2.1 Account Class with an Instance
Variable, a set Method and a get
Method
3.2.2 AccountTest Class That Creates
and Uses an Object of Class Account
3.2.3 Compiling and Executing an App with
Multiple Classes
3.2.4 Account UML Class Diagram with an
Instance Variable and set and get
Methods
3.2.5 Additional Notes on Class
AccountTest
3.2.6 Software Engineering with private
Instance Variables and public set
and get Methods

3.3 Primitive Types vs. Reference Types
3.4 Account Class: Initializing Objects
with Constructors
3.4.1 Declaring an Account Constructor
for Custom Object Initialization
3.4.2 Class AccountTest : Initializing
Account Objects When They're
Created
3.5 Account Class with a Balance;
Floating-Point Numbers
3.5.1 Account Class with a balance
Instance Variable of Type double
3.5.2 AccountTest Class to Use Class
Account
3.6 (Optional) GUI and Graphics Case
Study: Using Dialog Boxes
3.7 Wrap-Up

Summary | Self-Review Exercises | Answers to Self-Review Exercises | Exercises | Making a Difference

3.1 Introduction
[ Note: This chapter depends on the terminology and concepts of object-oriented program-
ming introduced in Section 1.5, Introduction to Object Technology.]
In Chapter 2, you worked with existing classes, objects and methods. You used the pre-
defined standard output object System.out , invoking its methods print , println and
printf to display information on the screen. You used the existing Scanner class to create
an object that reads into memory integer data typed by the user at the keyboard. Through-
out the topic, you'll use many more preexisting classes and objects—this is one of the great
strengths of Java as an object-oriented programming language.
In this chapter, you'll learn how to create your own classes and methods. Each new
class you create becomes a new type that can be used to declare variables and create objects.
You can declare new classes as needed; this is one reason why Java is known as an extensible
language.
We present a case study on creating and using a simple, real-world bank account
class— Account . Such a class should maintain as instance variables attributes such as its name
and balance , and provide methods for tasks such as querying the balance ( getBalance ),
making deposits that increase the balance ( deposit ) and making withdrawals that decrease
the balance ( withdraw ). We'll build the getBalance and deposit methods into the class in
the chapter's examples and you'll add the withdraw method in the exercises.
In Chapter 2 we used the data type int to represent integers. In this chapter, we intro-
duce data type double to represent an account balance as a number that can contain a dec-
imal point —such numbers are called floating-point numbers . [In Chapter 8, when we get a
bit deeper into object technology, we'll begin representing monetary amounts precisely with
class BigDecimal (package java.math ) as you should do when writing industrial-strength
monetary applications.]