Consider the following code fragment. The result of the entire pipeline is "ab" in all cases, as expected.

Stream.of("a", "ab", "abc", "abcd")
    // .sorted() // uncomment and what follows becomes eager
    .filter(s -> s.contains("b"))
    .peek(s -> System.out.println("PEEK: " + s))
    .findFirst()
    .orElse("X");

With sorted() commented out, findFirst() is fully lazy and so the output from peek is:

    PEEK: ab

However, with sorted() uncommented, the output changes to:

    PEEK: ab
    PEEK: abc
    PEEK: abcd

All the elements appear to be sent downstream from sorted() even though findFirst() is only interested in the first one. This could be a performance problem if the operations after sorted(), such as filtering, are expensive.

Workaround: collect the sorted results into a collection and run the rest of the pipeline from that collection.

See also: http://stackoverflow.com/q/23419223/1441122