4.22 Java4120: the comparator interface, part 4

Revised: Thu Apr 07 12:34:58 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
  • An array is a container
  • An opportune time
• Generics
• Discussion and sample code
  • Beginning with a quiz
    • Similar to previous programs
    • A new Vector object
    • A Vector is a List
    • The fillIt method
    • Iteration on a Vector
    • The output
  • The toArray method
    • The contract
    • Elements are returned in ascending index order
    • A "safe" array
    • Display the contents of the array
  • Sorting the array into natural order
    • The Comparable interface and polymorphic behavior
    • Display the sorted array data
    • The natural order for String objects
  • Sort the array with a Comparator
    • What does Oracle have to say about this?
    • The class named TheComparator
    • Display the array contents again
    • Could have sorted differently
  • Display the collection data again
  • The bottom line
• 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 extract the contents of a collection into an array, and how to use a Comparator object to sort the contents of the array into reverse natural order. The module also shows you how to sortthe contents of the array into natural order without the use of a Comparator object.

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 Comparator 05.
• Listing 2 . A new Vector object.
• Listing 3 . Call the fillIt method.
• Listing 4 . The fillIt method.
• Listing 5 . Iteration on a Vector.
• Listing 6 . Call the toArray method.
• Listing 7 . Display the contents of the array.
• Listing 8 . Sorting the array into natural order.
• Listing 9 . Display the sorted array data.
• Listing 10 . Sort the array with a Comparator.
• Listing 11 . The class named TheComparator.
• Listing 12 . Display the contents again.
• Listing 13 . Display the collection data again.

Preview

The primary purpose of recent modules in this series was to teach you about the interactions between the Comparator interface and the Collections Framework.

This module departs somewhat from that primary purpose and teaches you how to use a Comparator object to sort the contents of an array containing references to objects. Technically speaking, an array is not part ofthe core Collections Framework. However, it is definitely a first cousin to the Framework.