How many times have you read or written the same two or three lines of code that frequently seem to go together, and even though they operate on different objects, feel like the same thing? And how often these repetitions involve some sort of collections iteration or more generically manipulation? These repetitions in the code is something that developers eventually learn to filter out and ignore when reading code, once they figure out where the interesting parts are placed. But even if the developers get used to it, it slows them down. Code like that is clearly written for computers to execute, not for developers to read.
lambdaj is designed to easily manipulate collections. Its features are intended to filter, convert, index and aggregate the items of a collection without explicitly iterate on it.