Data Structures and Algorithms in Java[1].pdf - Fulvio Frisone

Figure 2.5 : Inheritance diagram for class
Progression and its subclasses.
To complete our example, we define a class TestProgression, shown in
Code Fragment 2.6, which performs a simple test of each of the three classes. In
this class, variable prog is polymorphic during the execution of the main
method, since it references objects of class ArithProgression,
GeomProgression, and FibonacciProgression in turn. When the main
method of the TestProgression class is invoked by the Java run-time
system, the output shown in Code Fragment 2.7 is produced.
The example presented in this section is admittedly small, but it provides a simple
illustration of inheritance in Java. The Progression class, its subclasses, and
the tester program have a number of shortcomings, however, which might not be
immediately apparent. One problem is that the geometric and Fibonacci
progressions grow quickly, and there is no provision for handling the inevitable
overflow of the long integers involved. For example, since 3 40 > 2 63 , a geometric
progression with base b = 3 will overflow a long integer after 40 iterations.
Likewise, the 94th Fibonacci number is greater than 2 63 ; hence, the Fibonacci
progression will overflow a long integer after 94 iterations. Another problem is
that we may not allow arbitrary starting values for a Fibonacci progression. For
example, do we allow a Fibonacci progression starting with 0 and −1 ? Dealing
with input errors or error conditions that occur during the running of a Java
program requires that we have some mechanism for handling them. We discuss
this topic next.
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