There are two types of stream operations: intermediate operations, which return another stream, and terminal operations, which return something other than a stream. Intermediate operations are lazy, meaning they aren’t actually executed until and unless a terminal stream operation is performed on their results. Consequently, if the result of an intermediate stream operation is not fed to a terminal operation, it serves no purpose, which is almost certainly an error.
widgets.stream().filter(b -> b.getColor() == RED); // Noncompliant
int sum = widgets.stream() .filter(b -> b.getColor() == RED) .mapToInt(b -> b.getWeight()) .sum(); Stream<Widget> pipeline = widgets.stream() .filter(b -> b.getColor() == GREEN) .mapToInt(b -> b.getWeight()); sum = pipeline.sum();