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15: Discovering Problems

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15: Discovering Problems

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15: Discovering Problems

Before C was tamed into ANSI C, we had a little joke: “My code compiles, so it should run!” (Ha ha!)

This was funny only if you understood C, because at that time the C compiler would accept just about anything; C was truly a “portable assembly language” created to see if it was possible to develop a portable operating system (Unix) that could be moved from one machine architecture to another without rewriting it from scratch in the new machine’s assembly language. So C was actually created as a side-effect of building Unix and not as a general-purpose programming language. Feedback

Because C was targeted at programmers who wrote operating systems in assembly language, it was implicitly assumed that those programmers knew what they were doing and didn’t need safety nets. For example, assembly-language programmers didn’t need the compiler to check argument types and usage, and if they decided to use a data type in a different way than it was originally intended, they certainly must have good reason to do so, and the compiler didn’t get in the way. Thus, getting your pre-ANSI C program to compile was only the first step in the long process of developing a bug-free program. Feedback

The development of ANSI C along with stronger rules about what the compiler would accept came after lots of people used C for projects other than writing operating systems, and after the appearance of C++, which greatly improved your chances of having a program run decently once it compiled. Much of this improvement came through strong static type checking: “strong” because the compiler prevented you from abusing the type, “static” because ANSI C and C++ perform type checking at compile time. Feedback

To many people (myself included), the improvement was so dramatic that it appeared that strong static type checking was the answer to a large portion of our problems. Indeed, one of the motivations for Java was that C++’s type checking wasn’t strong enough (primarily because C++ had to be backward-compatible with C, and so was chained to its limitations). Thus Java has gone even further to take advantage of the benefits of type checking, and since Java has language-checking mechanisms that exist at run time (C++ doesn’t; what’s left at run time is basically assembly language—very fast, but with no self-awareness), it isn’t restricted to only static type checking.[86] Feedback

It seems, however, that language-checking mechanisms can take us only so far in our quest to develop a correctly-working program. C++ gave us programs that worked a lot sooner than C programs, but often still had problems such as memory leaks and subtle, buried bugs. Java went a long way toward solving those problems, yet it’s still quite possible to write a Java program containing nasty bugs. In addition (despite the amazing performance claims always touted by the flaks at Sun), all the safety nets in Java added additional overhead, so sometimes we run into the challenge of getting our Java programs to run fast enough for a particular need (although it’s usually more important to have a working program than one that runs at a particular speed). Feedback

This chapter presents tools to solve the problems that the compiler doesn’t. In a sense, we are admitting that the compiler can take us only so far in the creation of robust programs, so we are moving beyond the compiler and creating a build system and code that know more about what a program is and isn’t supposed to do. Feedback

One of the biggest steps forward is the incorporation of automated unit testing. This means writing tests and incorporating those tests into a build system that compiles your code and runs the tests every single time, as if the tests were part of the compilation process (you’ll soon start relying upon them as if they are). For this book, a custom testing system was developed to ensure the correctness of the program output (and to display the output directly in the code listing), but the defacto standard JUnit testing system will also be used when appropriate. To make sure that testing is automatic, tests are run as part of the build process using Ant, an open-source tool that has also become a defacto standard in Java development, and CVS, another open-source tool that maintains a repository containing all your source code for a particular project. Feedback

JDK 1.4 introduced an assertion mechanism to aid in the verification of code at run time. One of the more compelling uses of assertions is Design by Contract (DBC), a formalized way to describe the correctness of a class. In conjunction with automated testing, DBC can be a powerful tool. Feedback

Sometimes unit testing isn’t enough, and you need to track down problems in a program that runs, but doesn’t run right. In JDK 1.4, the logging API was introduced to allow you to easily report information about your program. This is a significant improvement over adding and removing println( ) statements in order to track down a problem, and this section will go into enough detail to give you a thorough grounding in this API. This chapter also provides an introduction to debugging, showing the information a typical debugger can provide to aid you in the discovery of subtle problems. Finally, you’ll learn about profiling and how to discover the bottlenecks that cause your program to run too slowly. Feedback



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