Streams

Streams: pipelines that take elements from a source, such as a list or a file, pass them through steps like filter and map, and end in one result. A stream is neither a collection nor a loop, and most stream bugs come from treating it as one or the other. The central idea is laziness: nothing runs until the last step asks for a result. It covers intermediate and terminal operations, a pipeline over a list and over a file, how elements flow one at a time, map and flatMap, collectors, single use, and parallel streams. It leaves out writing custom collectors and spliterators.