This book isn't an introduction to object-oriented technology or design.
Many books already do a good job of that.
On the other hand, this isn't an advanced technical treatise either. It's a book of design patterns that describes simple and elegant solutions to specific problems in object-oriented software design. Design patterns capture solutions that have developed and evolved over time. Hence they aren't the designs people They reflect untold redesign and recoding as developers have struggled for greater reuse and flexibility in their software. Design patterns capture these solutions in a succinct and easily applied form.