Latest Thinking In Java Articles - Page 5

6: Reusing classes

One of the most compelling features about Java is code reuse . But to be revolutionary, you’ve got to be able to do a lot more than copy code and change it.

Combining composition

It is very common to use composition and inheritance together. The following example shows the creation of a more complex class, using both inheritance and composition, along with the necessary constructor initialization:

Inheritance syntax

Inheritance is such an integral part of Java (and OOP languages in general) that it was introduced in Chapter 1 and has been used occasionally in chapters before this one because certain situations required it. In addition, you’re always doing inheritance when you create a class, because if you don’t say otherwise you inherit from Java’s standard root class Object .

protected

Now that you’ve been introduced to inheritance, the keyword protected finally has meaning. In an ideal world, private members would always be hard-and-fast private , but in real projects there are times when you want to make something hidden from the world at large and yet allow access for members of derived classes. The protected keyword is a nod to pragmatism. It says “This is private as far as the class user is concerned, but available to anyone who inherits from this class or anyone else in the same package .” That is, protected in Java is automatically “friendly.”

Summary

Both inheritance and composition allow you to create a new type from existing types. Typically, however, you use composition to reuse existing types as part of the underlying implementation of the new type and inheritance when you want to reuse the interface. Since the derived class has the base-class interface, it can be upcast to the base, which is critical for polymorphism, as you’ll see in the next chapter.

Upcasting

The most important aspect of inheritance is not that it provides methods for the new class. It’s the relationship expressed between the new class and the base class. This relationship can be summarized by saying “The new class is a type of the existing class.”

Latest Developer Videos

More...

Latest CodeGuru Developer Columns

MFC Integration with the Windows Transactional File System (TxF)

The Transactional File System (TxF), which allows access to an NTFS file system to be conducted in a transacted manner through extensions to the Windows SDK API. MFC 10, has been extended to support TxF and related technologies. This support allows existing MFC applications to be easily extended to support kernel transactions.

The Sorry State of .NET ORMs

Looking to work with a non Microsoft Database in .NET? You need to know what ORM's are available, and why you can't currently use Entity Framework.

Top White Papers and Webcasts

  • Packaged application development teams frequently operate with limited testing environments due to time and labor constraints. By virtualizing the entire application stack, packaged application development teams can deliver business results faster, at higher quality, and with lower risk.

  • Live Event Date: August 19, 2014 @ 11:00 a.m. ET / 8:00 a.m. PT You deployed your app with the Bluemix PaaS and it's gaining some serious traction, so it's time to make some tweaks. Did you design your application in a way that it can scale in the cloud? Were you even thinking about the cloud when you built the app? If not, chances are your app is going to break. Check out this upcoming webcast to learn various techniques for designing applications that will scale successfully in Bluemix, for the …

Most Popular Programming Stories

More for Developers

Latest Developer Headlines

RSS Feeds