4.28 Java4150: the toarray method, part 1

Revised: Fri Apr 08 11:29:38 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 ...
  • A new LinkedList collection
    • The LinkedList class
    • Populating the LinkedList collection
    • Four buttons and two labels
    • The toolTipText property
    • Why am I using Swing GUI components?
  • Making the objects distinguishable
    • Identifying the buttons and labels
    • Why populate this way?
    • Display the collection
    • Downcast is required
    • The output for the collection
  • Copy collection elements into an array
    • The toArray method
    • Display the array contents
    • The showArray method
    • The output for the array
  • How "safe" is the array?
    • Array contains copies of references to objects
    • Modifying the state of an object
    • Display array contents after object modification
    • Display the contents of the collection 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 use the simpler version of the overloaded toArray method that is declared in the Collection interface. The module also explains why you need to exercise care when using the elements stored in the resulting array to avoid corrupting the state of the objects referred to by the elements in the collection.

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 ToArray01.
• Listing 2 . A new LinkedList collection.
• Listing 3 . Beginning of the fillIt method.
• Listing 4 . Making the objects distinguishable.
• Listing 5 . The showCollection method.
• Listing 6 . Copy collection elements into an array.
• Listing 7 . Display the array contents.
• Listing 8 . The showArray method.
• Listing 9 . Modifying the state of an object.
• Listing 10 . Display the contents of the collection again.

Preview

In earlier modules, I used the toArray method, declared in the Collection interface, to copy elements from a collection into an array. However, in those modules, I didn't take the time to fully explain how to usethe method. Also, I didn't fully explain the precautions that you need to take when you use the method.