4.2 Java4020: what is a collection

Revised: Tue Apr 05 14:25:01 CDT 2016

This page is included in the following Books:

• ITSE 2321 - Object-Oriented Programming (Java)
• Object-Oriented Programming (OOP) with Java

Table of contents

• Preface
• Preview
• Generics
• Discussion
  • What is a collection?
  • Slightly different terminology
  • Store references rather than objects
  • Stored as type Object
  • Moving data among methods
  • Polymorphic behavior
  • Core collection interfaces
  • Concrete implementations
  • Iterator is not a class
  • What about Attributes and RenderingHints?
  • What is a Collections Framework?
• Summary
• Miscellaneous

Preface

This module is one of a series of modules designed to teach you about Object-Oriented Programming (OOP) in general and the Java Collectionsframework in particular.

The purpose of this module is to explain some of the details surrounding the use of a Java collection for creating data structures. The module also discusses the interfaces and some of the concrete implementations in the Java Collections Framework.

In addition to studying these modules, I strongly recommend that you study the Collections Trail in Oracle's Java Tutorials . The modules in this collection are intended to supplement and not to replace those tutorials.

Preview

Collection is not only the name of a Java interface, it is also the term given to an object that groups multiple elements into a single unit.

I will discuss the advantages of passing collections between methods as type Collection .

I will summarize the core interfaces in the Collections Framework and show you how they are related.

I will very briefly discuss some of the concrete implementations of the interfaces that are provided by the framework.

And finally, I will introduce you to the three kinds of things that are part of a collections framework.

Generics

The code in this series of modules is written with no thought given to Generics . As a result, if you copy and compile the code, you will probably get warnings about unchecked or unsafe operations .

While you will ultimately need to understand how to use Generics, that is avery complex topic. An understanding of Generics is beyond the scope of this course. Therefore, for purposes of this course, you can simply ignore thosewarnings.

Discussion

What is a collection?

Just to see if you are awake today, let's start with a little quiz.

What is a collection insofar as Java programming is concerned?

• A. Something they gather in plates at church.
• B. An object that groups multiple elements into a single unit.
• C. The name of a Java interface.
• D. None of the above.

If you answered A, you are probably reading an article on the wrong website by mistake. If you answered Both B and C , then you are off to a good start on this module.

Collection is the name of a Java interface. This interface is an integral part of the Java Collections Framework . Collection is one of two top-level interfaces in the framework. The other top-level interfacein the framework is named Map .