4.26 Java4140: the comparator interface, part 6

Revised: Fri Apr 08 11:08:24 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
  • Viewing tip
    • Listings
• Preview
• Generics
• Discussion and sample code
  • Beginning with a quiz
    • And the answer is ...
    • Similar to previous programs
    • A new ArrayList object
    • Displays the list contents
    • The ArrayList class
    • The reverse method of the Collections class
  • The Collections class
    • The reverse method
    • Contents of the list
    • The reverseOrder method
    • What does Oracle have to say about this?
    • Reverse natural order
  • A type-independent Comparator
    • The wonderful world of the Java interface
    • Sorting the list
    • Source of Comparator object is new
    • Don't know, don't care
    • The output
• Run the program
• 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.

This module shows you how to use a Comparator created by the reverseOrder method of the Collections class to sort a list into reverse natural order. The module also shows you how to use the reverse method of the Collections class to reverse the order of the elements in a list.

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.

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 listings while you are reading about them.

Listings

• Listing 1 . The program named Comparator07.
• Listing 2 . A new ArrayList object.
• Listing 3 . The fillIt method.
• Listing 4 . The reverse method of the Collections class.
• Listing 5 . The reverseOrder method.
• Listing 6 . Sorting the list.
• Listing 7 . Produce the output.

Preview

In this module, I will teach you how to use a Comparator created by the reverseOrder method of the Collections class to sort a list into reverse natural order . I will also teach you how to use the reverse method of the Collections class to reverse the order of the elements in a list.

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 a very complex topic. An understanding of Generics is beyond the scope of thiscourse. Therefore, for purposes of this course, you can simply ignore those warnings.

Discussion and sample code

Beginning with a quiz

Let's begin with a quiz to test your prior knowledge of the Collections Framework.