Java Reference
In-Depth Information
From a class developer's perspective, a class is designed for use by many different customers.
In order to be useful in a wide range of applications, a class should provide a variety of ways
for customization through constructors, properties, and methods.
The
Loan
class contains two constructors, four
get
methods, three
set
methods, and the
methods for finding the monthly payment and the total payment. You can construct a
Loan
object by using the no-arg constructor or the constructor with three parameters: annual inter-
est rate, number of years, and loan amount. When a loan object is created, its date is stored in
the
loanDate
field. The
getLoanDate
method returns the date. The three
get
methods—
getAnnualInterest
,
getNumberOfYears
, and
getLoanAmount
—return the annual
interest rate, payment years, and loan amount, respectively. All the data properties and meth-
ods in this class are tied to a specific instance of the
Loan
class. Therefore, they are instance
variables and methods.
Important Pedagogical Tip
Use the UML diagram for the
Loan
class shown in Figure 10.4 to write a test program
that uses the
Loan
class even though you don't know how the
Loan
class is imple-
mented. This has three benefits:
■
It demonstrates that developing a class and using a class are two separate tasks.
■
It enables you to skip the complex implementation of certain classes without inter-
rupting the sequence of this topic.
■
It is easier to learn how to implement a class if you are familiar with it by using the class.
For all the class examples from now on, create an object from the class and try using its
methods before turning your attention to its implementation.
10.8
✓
✓
If you redefine the
Loan
class in Listing 10.2 without
set
methods, is the class
immutable?
Check
Point
The procedural paradigm focuses on designing methods. The object-oriented
paradigm couples data and methods together into objects. Software design using the
object-oriented paradigm focuses on objects and operations on objects.
Key
Point
Chapters 1-7 introduced fundamental programming techniques for problem solving using
loops, methods, and arrays. Knowing these techniques lays a solid foundation for object-
oriented programming. Classes provide more flexibility and modularity for building reusable
software. This section improves the solution for a problem introduced in Chapter 3 using the
object-oriented approach. From these improvements, you will gain insight into the differences
between procedural and object-oriented programming and see the benefits of developing
reusable code using objects and classes.
Listing 3.5, ComputeAndInterpretBMI.java, presented a program for computing body
mass index. The code cannot be reused in other programs, because the code is in the
main
method. To make it reusable, define a static method to compute body mass index as follows:
public static double
getBMI(
double
weight,
double
height)
This method is useful for computing body mass index for a specified weight and height. How-
ever, it has limitations. Suppose you need to associate the weight and height with a person's
name and birth date. You could declare separate variables to store these values, but these val-
ues would not be tightly coupled. The ideal way to couple them is to create an object that con-
tains them all. Since these values are tied to individual objects, they should be stored in
instance data fields. You can define a class named
BMI
as shown in Figure 10.5.
