The Java Query Language (JQL)
JQL is an extension for Java that provides support for querying objects across collections (similar to Python's list comprehensions) and also their extent sets (i.e. the set of all allocated objects of the given class). Queries provide a powerful abstraction for operating on object subsets determined by a query expression (e.g. all Students where age < 3). The query engine takes care of efficiently searching the source set to identify those matching the query expression and uses several well-known database techniques (e.g. using hash joins, sorted joins and selecting good join orders) for this purpose. This results in shorter, clearer code that is typically also more efficient than the average programmer might produce by hand.