Java4210: getting started with generics

Revised: Wed May 11 17:07:35 CDT 2016

This page is included in the following Books:

• ITSE2317 - Java Programming (Intermediate)
• Object-Oriented Programming (OOP) with Java

Table of Contents

• Table of Contents
• Preface
  • Viewing tip
    • Figures
    • Listings
• General background information
• Preview
• Discussion and sample code
  • Collection behavior prior to Java version 1.5
  • An incorrect cast in code that doesn't use generics
  • Dealing with angle brackets in cnxml body text
  • Avoiding the requirement to cast through the use of generics
  • Compile-time type safety provided by the use of generics
  • Generic iterator syntax and the enhanced for loop
• Run the programs
• Summary
• What's next?
• Miscellaneous
• Complete program listings

Preface

This module is one in a collection of modules on Java Generics designed for teaching ITSE2317 - Java Programming (Intermediate) at Austin Community College in Austin, TX.

Many new features in Java version 1.5

When Java version 1.5 was released, it contained many new language features, including:

• Generics
• Enhanced for Loop
• Autoboxing/Unboxing
• Typesafe Enums
• Varargs
• Static Import
• Metadata

In addition to the new language features, Java version 1.5 also contained other new features such as new Look and Feel capabilities for Swing GUIs.

First in a series

This is the first module in a series of modules designed to teach you about Generics in Java version 1.5. Thismodule will teach you some of the rudimentary aspects of the generics capability . This module will also teach you how to use the enhanced for loop with collections.

Future modules will teach you how to use other aspects of generics

Viewing tip

I recommend that you open another copy of this module in a separate browser window and use the following links to easily find and view the Figuresand the Listings while you are reading about them.

Figures

• Figure 1 . Typical v1.5 compiler warning.
• Figure 2 . Warning with -Xlint:unchecked.
• Figure 3 . A ClassCastException.
• Figure 4 . A compiler error.
• Figure 5 . Iterator output.

Listings

• Listing 1 . Beginning of the program named Generics05.
• Listing 2 . Beginning of the runIt method.
• Listing 3 . An iterator.
• Listing 4 . Enhanced for loop.
• Listing 5 . The program named Generics01.
• Listing 6 . The program named Generics02.
• Listing 7 . The program named Generics03.
• Listing 8 . The program named Generics04.
• Listing 9 . The program named Generics05.

General background information

A new compiler warning

Have you recently tried to recompile a legacy program that has compiled and executed properly for many years only to get a compiler message similar to thatshown in Figure 1 ?

If you followed up and recompiled as directed, you probably got a message from the compiler that looked something like the one shown in Figure 2 .