Graham Hardman

A First Look

Java is big. As you learn more about it you will come to realise just how true this is. Java is a truly general-purpose programming language; you could use a program written in Java for just about anything from flying an airliner to keeping track of numbers on a mobile phone. This is good, because you are going to learn a powerful language with many useful applications. But it is also bad because it’s difficult to know where to start. There really is a lot going on in even the simplest Java program.

Classes and Objects

You’ve now seen quite a lot of Java. You’ve seen how to create a class and how to create instances of the class (objects), and how to use these objects in very simple programs. This has all been a bit informal, though, so the time has come to have a proper look and to get some practice in writing your own programs. This chapter and the last one start you on the way to doing that.

A Word on Testing

You have now written your first complete Java program. Most of the rest of this book will be about Java, but in many ways writing a program is only half of the story. If a program is going to be truly useful the programmer and, more importantly, the program’s intended final users must have confidence in the results that it produces. They must be sure that the results they see from the program are correct. Business users are potentially going to base costly business decisions on the results produced by the programs they use, pilots are going to trust navigational systems in their aircraft, and so on. This brings us to a brief pause from looking at Java. This chapter looks briefly at how and why computer programs are tested.

Objects The Building Block

You already know that Java is an object-oriented programming language. Many other currently popular programming languages including C+ +, Python, and C# also use this object-oriented approach. This means, not surprisingly, that programming in Java (and these other languages) is based around the use of objects; objects are the basic building block of any object-oriented computer program. Java takes the idea further than some other object-oriented languages to the extent that almost everything in a Java program is an object; even the Java program itself looks rather like an object (even if it isn’t actually one).

Making Things Happen. Sometimes

Up to this point the behaviour of your programs has been very predictable. The programs have been simply a sequence of statements that is executed in a strict order from the top of the program to the bottom. While you have been able to accept input values from your users all you have been able to do is use these values in calculations. You have not been able to use them as the basis of decisions. More complex programs take values from the user and will behave differently depending on the values that are entered. This chapter is about writing programs that do just that; they take values, test conditions, and then behave differently depending on the results.

A First Class

Up to now, we have looked at some basic objects, given them a moderate amount of functionality, and learned how to use these objects in simple programs. This book was never intended to be that basic, so in the next two chapters we shall revisit much of the earlier material, going into greater depth about classes, objects, methods, and attributes.

More on Tesling

This is very nearly the end of the book. You have now seen all the Java that you are going to see in detail. You should by now be able to write quite complex Java programs making use of many of the features available in the current versions of Java. You should be able to analyse a problem and then go on to design and develop the classes and programs that will form the basis of a solution.

Programmin (Don’t Panic!)

The time has come when you are almost ready to start using Java to write some programs. Before you do, though, you need to understand something about the process of programming. Programming is a highly structured process; some might even call it a discipline. Good programming requires that the programmer adopt a sensible, structured, and measured approach. Above all it requires that the programmer doesn’t panic!

A word on Analsis & Design

The exercises in the previous chapter introduced you informally to the task of identifying objects in a real-world problem. You should now have some experiencing of suggesting the objects that might be used in a program to solve some problem; you should also be able to make some suggestions for possible attributes and methods of the objects you identify.

What this book is

Good Evening. Glad you could make it. Pull up a chair. Just let me put some more logs on the fire. Move the papers off the stool. Help yourself to a drink from the cabinet; there’s some orange juice at the back, and maybe something stronger somewhere. I’m afraid I’ve run out of toast and pretzels. Would you like a chocolate digestive?