Java4210: getting started with generics

Not quite as powerful as an iterator

Although not shown in Listing 3 , the use of an iterator allows you to remove the most recently accessed element from a collection. As near as I cantell, the enhanced for loop does not provide that capability. Therefore, the enhanced for loop is not quite as powerful as an iterator. However, if you don't need to remove elements from the collection, the enhanced for loop appears to be a good and somewhat simpler alternative to an iterator.

The output

The code in Listing 4 produced the last three lines of text in the output shown in Figure 5 . Obviously the last three lines match the first three lines since they simply represent different ways to produce a textrepresentation of the same three Date objects.

Run the programs

I encourage you to copy the code from Listing 5 through Listing 9 Compile the code and execute it. Experiment with the code,making changes, and observing the results of your changes. Make certain that you can explain why your changes behave as they do.

Summary

In this module, I explained:

• How the Java Collections Framework behaved prior to the release of Java version 1.5.
• The effect of an incorrect cast in code that doesn't use generics.
• How to avoid the requirement to cast through the use of generics, including an illustration of some of the required syntax for generics.
• The compile-time type safety provided by the use of generics.
• The syntax requirements for the use of iterators with generics.
• The use of the enhanced for loop with collections.

What's next?

Future modules in this series will be based on the Generics (Updated) section of The Java Tutorials from Oracle. (In the event that these links become broken, you should have no difficulty finding the Oracle material with an online search.)

Those modules will teach you about other aspects of generics including:

• Generic methods
• Generic classes
• Raw types in generics
• Wildcards and bounded wildcards in generics
• The impact of inheritance on generics

Miscellaneous

This section contains a variety of miscellaneous information.