Add a PDF URL to a recently removed HTML version of a book

[cchaduka]

What does this PR do?

Add resource(s)

IMPORTANT

• Read our contributing guidelines.
• Is this a revision of a previously submitted PR? If so, STOP! Go back, reopen the PR, and add commit(s) the branch you previously submitted. Please don't make the job of reviewing more difficult by hiding previous work.

For resources

Description

A recent commit removed a link to a an HTML OOP book resource. This PR provides a link to the PDF version.

Why is this valuable (or not)?

The resource teaches Object-Oriented Programming in Java.

How do we know it's really free?

The second page of the PDF file states that it is under the Creative Commons Licence and users are free to distribute it, among other allowed activities.

For book lists, is it a book? For course lists, is it a course? etc.

This is a book.

Checklist:

• Search for duplicates.
• Include author(s) and platform where appropriate.
• Put lists in alphabetical order, correct spacing.
• Add needed indications (PDF, access notes, under construction).
• Used an informative name for this pull request.

Follow-up

• Check the status of GitHub Actions and resolve any reported warnings!

[rdhyee]

Hi @cchaduka! Thanks for finding an alternative URL for this book!

Context:
The HTML version of this book was removed 2 days ago (PR #12667) due to a 403 Forbidden error on the original URL.

Verification:

• ✅ PDF is accessible at the new URL
• ✅ Same book/author (Richard L. Halterman)
• ✅ All linter checks passing
• ✅ Proper formatting with license info (CC)

This is a good find - bringing back a resource that was recently lost. Labeling for final review and merge!