ABAP Objects -the book on modern ABAP - is co-authored by Dr. Horst Keller and Sascha Kruger. To give you a background, there was a book 'ABAP Objects - An Introduction to Programming SAP Applications' published way back in year 2000 from the same authors.
That was the time of SAP Release 4.6 when object-oriented features were being gradually added starting from Release 4.0. So basically the first book applied fully to Release 4.6. Since many of the features for Release 4.6 - object-oriented and other additions to regular ABAP also - are still there and many were further enhanced in later releases, still that book is not outdated. If you have a copy of that book it's okay to use it.
But this new book covers many of the advanced features accumulated by ABAP language over time as the language is under constant change since then. There are important additions after Release 4.6x which naturally are not a part of the earlier book. SAP ABAP has covered a long distance since Release 4.6 with many milestones. The current book is applicable to SAP Release ECC 7.0 and discusses the concepts of modern ABAP including many new features added during the course of its journey to this release.
This is a 1000+ page book and comes with SAP installation DVDs which will help you to install SAP Netweaver developer version on your system.
If you don't have access to an SAP system, this is a real help ! That way, you can create programs following the book and that's the recommended approach.
One interesting point on the choice of authors by SAP: Dr Horst Keller is an SAP employee and Sascha Kruger is an external consultant. Seems they wanted this book to be a blend of views from the developers of ABAP language inside SAP and the implementers of the language in real-business.
There are many ABAP books which initiate your learning into ABAP. But this is probably the best book so far. I would recommend it very strongly to the beginners and the experienced ABAP developers alike.
For beginners, it launches you so smoothly into learning ABAP that from the outset you have a broad view of the ABAP programming language.
And for the experienced, this book will give you a fresh outlook on many common features of application programming, add on to your skill set the newly introduced features and a sneak-preview of Release 7.10. And yes ... for reference whenever you need it on the job !