4.10 Java4060: duplicate elements, ordered collections, sorted

Revised: Wed Apr 06 09:47:48 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
  • We will start with a quiz
  • The root of the Collection hierarchy
    • What does Oracle say about this?
  • What about duplicate elements?
  • What is a set?
  • What is a list?
  • Ordered is not the same as sorted
  • Is ascending sort order always required?
    • Does case matter in String objects?
  • Sub-interfaces have more stipulations
    • Stipulations on set
    • Stipulations on SortedSet
  • We will end with a quiz
    • Question 1
    • Question 2
    • Question 3
    • Question 4
• Summary
• What's next?
• 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.

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

You learned in earlier modules that the Java Collections Framework defines eight core interfaces, in two distinct trees.One of the trees, which consists of six interfaces, is rooted in the interface named Collection . The other tree, which consists of two interfaces, isrooted in the interface named Map .

You learned the names and the inheritance structure of those interfaces. You also learned about theirpurpose. You saw how the interfaces declare polymorphic methods that apply to implementations of the interfaces, and you learned about the optional methods ofthe Collection interface and the Map interface.

In this module you will learn that all of the implementations of the interfaces on the Collection side of the Java Collections Framework (the Collection hierarchy) implement one of the sub-interfaces of the Collection interface. (A similar discussion regarding the Map side of the Java Collections framework will be deferred until a future module.)

You will learn that a Set object cannot contain duplicate elements, but a List object can contain duplicate elements.

You will learn about the difference between ordered collections and sorted collections. You will also learn about ascending order and the natural ordering of objects.

In addition, you will learn how more specialized stipulations are placed on interfaces as you progress downthe interface inheritance hierarchy of the Java 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 .