Java Reference
In-Depth Information
Software Engineering Observation 6.1
Familiarize yourself with the rich collection of classes and methods provided by the Java
common packages. Online Appendix F explains how to navigate the API documentation.
Don't reinvent the wheel. When possible, reuse Java API classes and methods. This reduces
program development time and avoids introducing programming errors.
Divide and Conquer with Classes and Methods
Classes and methods help you modularize a program by separating its tasks into self-con-
tained units. The statements in the method bodies are written only once, are hidden from
other methods and can be reused from several locations in a program.
One motivation for modularizing a program into classes and methods is the
divide-
and-conquer
approach, which makes program development more manageable by con-
structing programs from small, simple pieces. Another is
software reusability
—using
existing classes and methods as building blocks to create new programs. Often, you can
create programs mostly from existing classes and methods rather than by building custom-
ized code. For example, in earlier programs, we did not define how to read data from the
keyboard—Java provides these capabilities in the methods of class
Scanner
. A third moti-
vation is to
avoid repeating code
. Dividing a program into meaningful classes and methods
makes the program easier to debug and maintain.
Software Engineering Observation 6.2
To promote software reusability, every method should be limited to performing a single,
well-defined task, and the name of the method should express that task effectively.
Error-Prevention Tip 6.1
A method that performs one task is easier to test and debug than one that performs many tasks.
Software Engineering Observation 6.3
If you cannot choose a concise name that expresses a method's task, your method might be
attempting to perform too many tasks. Break such a method into several smaller ones.
Hierarchical Relationship Between Method Calls
As you know, a method is invoked by a method call, and when the called method com-
pletes its task, it returns control and possibly a result to the caller. An analogy to this pro-
gram structure is the hierarchical form of management (Fig. 6.1). A boss (the caller) asks
a worker (the called method) to perform a task and report back (return) the results after
completing the task. The boss method does not know how the worker method performs
its designated tasks. The worker may also call other worker methods, unbeknown to the
boss. This “hiding” of implementation details promotes good software engineering.
Figure 6.1 shows the
boss
method communicating with several worker methods in a hi-
erarchical manner. The
boss
method divides its responsibilities among the various
worker
methods. Here,
worker1
acts as a “boss method” to
worker4
and
worker5
.
Error-Prevention Tip 6.2
When you call a method that returns a value indicating whether the method performed
its task successfully, be sure to check the return value of that method and, if that method
was unsuccessful, deal with the issue appropriately.
