2.11 Jb0150: java oop: a gentle introduction to java data types  (Page 9/9)

• Suzie Smith
• Suzie Jones,
• Suzie Smith-Jones,
• Suzie Jones-Smith, or
• something entirely different.

In this case, there would be a need to modify the object that represents Suziein order to reflect her newly-elected surname. (Or perhaps Tom Jones might elect to thereafter be known as Tom Jones-Smith, in which case it would be necessary to modify the object that represents him.)

An updated telephone book

The person charged with maintaining the database could

• use the name-changing operation to modify the object and change the name,
• make use of the sorting operation to re-sort the set of objects, and
• print and distribute an updated version of the telephone book.

Many user-defined types already exist

Unlike the primitive types which are predefined in the core language, I am unable to give you much in the way of specific information about user-defined types, simply because they don't exist until a user defines them.

I can tell you, however, that when you obtain the Java programming tools from Sun, you not only receive the core language containing the primitive types, you also receive a large library containing several thousand user-defined types that have already been defined. A large documentation package is available from Sun to help you determine the individual characteristics of these user-defined types.

The most important thing

At this stage in your development as a Java programmer, the most important thing for you to know about user-defined types is that they are possible.

You can define new types. Unlike earlier procedural programming languages such as C and Pascal, you are no longer forced to adapt your problem to the available tools. Rather, you now have the opportunity to extend the tools to make them better suited to solve your problem.

The class definition

The specific mechanism that makes it possible for you to define new types in Java is a mechanism known as the class definition .

In Java, whenever you define a new class, you are at the same time defining a new type. Your new type can be as simple, or as complex and powerful as you want it to be.

An object (instance) of your new type can contain a very small amount of data, or it can contain a very large amount of data. The operations that you allow to be performed on an object of your new type can be rudimentary, or they can be very powerful.

It is all up to you

Whenever you define a new class (type) you not only have the opportunity to define the data definition and the operations, you also have a responsibility to do so.

Much to learn and much to do

But, you still have much to learn and much to do before you will need to define new types.

There are a lot of fundamental programming concepts that we will need to cover before we seriously embark on a study involving the definition of new types.

For the present then, simply remember that such a capability is available, and if you work to expand your knowledge of Java programming one small step at a time, when we reach the point of defining new types, you will be ready and eager to do so.

Sample program

I'm not going to provide a sample program in this module. Instead, I will be using what you have learned about Java data types in the sampleprograms in future modules.

Miscellaneous

This section contains a variety of miscellaneous information.

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