Introduction tells you what collections are, and how they'll make your job easier and your programs better. You'll learn about the core elements that comprise the Collections Framework: interfaces, implementations and algorithms.
Interfaces describes the core collection interfaces, which are the heart and soul of the Java Collections Framework. You'll learn general guidelines for effective use of these interfaces, including when to use which interface. You'll also learn idioms for each interface that will help you get the most out of the interfaces.
Implementations describes the JDK's general-purpose collection implementations and tells you when to use which implementation. You'll also learn about the wrapper implementations, which add functionality to general-purpose implementations.
Algorithms describes the polymorphic algorithms provided by the JDK to operate on collections. With any luck you'll never have to write your own sort routine again!
Custom Implementations tells you why you might want to write your own collection implementation (instead of using one of the general-purpose implementations provided by the JDK), and how you'd go about it. It's easy with the JDK's abstract collection implementations!
Interoperability tells you how the Collections Framework interoperates with older APIs that predate the addition of Collections to Java. Also, it tells you how to design new APIs so that they'll interoperate seamlessly with other new APIs.