Well-behaved objects - Objects First with Java: A Practical Introduction Using BlueJ - page 236

CHAPTER
7

Well-behaved objects

Main concepts discussed in this chapter:

■ testing

■ debugging

■ unit testing

■ test automation

Java constructs introduced in this chapter:

(No new Java constructs are introduced in this chapter.)

7.1 Introduction

If you have followed the previous chapters in this topic and if you have implemented the
exercises we have suggested, then you have written a good number of classes by now. One
observation that you will likely have made is that a class you write is rarely perfect after
the first attempt to write its source code. Usually, it does not work correctly at first, and some
more work is needed to complete it.

The problems you are dealing with will shift over time. Beginners typically struggle with Java
syntax errors. Syntax errors are errors in the structure of the source code itself. They are easy to
spot, because the compiler will highlight them and display some sort of error message.

More-experienced programmers who tackle more-complicated problems usually have less dif-
ficulty with the language syntax. They are more concerned with logical errors instead.

A logical error is a problem where the program compiles and executes without an obvious error
but delivers the wrong result. Logical problems are much more severe and harder to find than
syntax errors. In fact, it is sometimes not easy to detect that there even is an error in the first place.

Writing syntactically correct programs is relatively easy to learn, and good tools (such as com-
pilers) exist to detect syntax errors and point them out. Writing logically correct programs, on
the other hand, is very difficult for any nontrivial problem, and proof that a program is correct
cannot, in general, be automated. It is so hard, in fact, that most software that is sold commer-
cially is known to contain a significant number of bugs.

Thus, it is essential for a competent software engineer to learn how to deal with correctness and
how to reduce the number of errors in a class.