Reviews : Java Books :
Beginning Java Objects : Chapters 2 and 3

Buy this book Title: Beginning Java Objects ISBN: 1861004176 US Price: $ 39.99 Canadian Price: C$ 59.95 UK Price: £ 28.99 Publication Date: November 2000 Pages: 800 © Wrox Press Limited, US and UK.

Three Distinguishing Features of an
Object-Oriented Programming Language

In order to be considered truly object oriented, a programming language must provide support for three key mechanisms:

• (Programmer creation of) Abstract Data Types (ADTs)
• Inheritance
• Polymorphism

We've just learned about the first of these — ADTs — and will discuss the other two in chapters to follow.

Summary

In this chapter, we've learned that:

• An object is a software abstraction of a physical or conceptual real-world object.
• A class serves as a template for defining objects: specifically, a class defines:
• What data the object will house, known as an object's attributes.
• What behaviors or services an object will be able to perform, known as an object's operations or methods.
• An object may then be thought of as a filled-in template, where attribute values have been provided.
• Just as we can declare variables to be of simple built-in data types such as int, float, and char, we can also declare variables to be of an abstract data type, based on the classes that we define. Such variables are known as reference variables, or simply references.
• When we create a new object (a process known as instantiation), we store a handle on that object in a reference variable. We can then use that handle to communicate with the object.
• We can define attributes of a class 'A' to be references to objects belonging to another class 'B'. In doing so, we allow each object to encapsulate the information that rightfully belongs to that object, but enable objects to share information by contacting one another whenever necessary.

Exercises

1. From the perspective of an academic setting (and not necessarily the SRS case study), think about what the appropriate attributes and methods of the following classes might be:

• Classroom
• Department
• Degree

Which of the attributes of each of these classes might be declared as built-in Java data types, and which might be declared as abstract data types? Explain your rationale.

2. For the problem area whose requirements you defined for exercise no. 3 in Chapter 2, list the abstract data types/classes that you might need to model.

3. List the abstract data types/classes that you might need to model for the Conference Room Reservation System discussed in Appendix B.

4. Would 'Color' make a good abstract data type? Why or why not?

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