GuavaExplained - guava-libraries
Every Java developer should read this wiki in detail.
The Guava project contains several of Google's core libraries that we rely on in our Java-based projects: collections, caching, primitives support, concurrency libraries, common annotations, string processing, I/O, and so forth. Each of these tools really do get used every day by Googlers.
But trawling through Javadoc isn't always the most effective way to learn how to make best use of a library. Here, we provide readable and pleasant explanations of some of the most popular and most powerful features of Guava.
This wiki is a work in progress, and parts of it may still be under construction.
Basic utilities: Make using the Java language more pleasant.
Preconditions: Test preconditions for your methods more easily.
Common object methods: Simplify implementing Object methods, like hashCode() and toString().
Ordering: Guava's powerful "fluent Comparator" class.
Throwables: Simplify propagating and examining exceptions and errors.
Collections: Guava's extensions to the JDK collections ecosystem. These are some of the most mature and popular parts of Guava.
Immutable collections, for defensive programming, constant collections, and improved efficiency.
New collection types, for use cases that the JDK collections don't address as well as they could: multisets, multimaps, tables, bidirectional maps, and more.
Powerful collection utilities, for common operations not provided in java.util.Collections.
Extension utilities: writing a Collection decorator? Implementing Iterator? We can make that easier.
Caches: Local caching, done right, and supporting a wide variety of expiration behaviors.
Functional idioms: Used sparingly, Guava's functional idioms can significantly simplify code.
Concurrency: Powerful, simple abstractions to make it easier to write correct concurrent code.
ListenableFuture: Futures, with callbacks when they are finished.
Service: Things that start up and shut down, taking care of the difficult state logic for you.
Strings: A few extremely useful string utilities: splitting, joining, padding, and more.
Primitives: operations on primitive types, like int and char, not provided by the JDK, including unsigned variants for some types.
Ranges: Guava's powerful API for dealing with ranges on Comparable types, both continuous and discrete.
I/O: Simplified I/O operations, especially on whole I/O streams and files, for Java 5 and 6.
Hashing: Tools for more sophisticated hashes than what's provided by Object.hashCode(), including Bloom filters.
EventBus: Publish-subscribe-style communication between components without requiring the components to explicitly register with one another.
Math: Optimized, thoroughly tested math utilities not provided by the JDK.
Reflection: Guava utilities for Java's reflective capabilities.