[FIXED] Remove first(with zero index) element from stream conditionally

Issue

I have following code:

Stream<String> lines = reader.lines();

If fist string equals "email" I want to remove first string from the Stream. For other strings from the stream I don't need this check.

How could I acheve it?

P.S.

Sure I can transform it to the list, then use old school for loop but further I need stream again.

Solution

While the reader will be in an unspecified state after you constructed a stream of lines from it, it is in a well defined state before you do it.

So you can do

String firstLine = reader.readLine();
Stream<String> lines = reader.lines();
if(firstLine != null && !"email".equals(firstLine))
    lines = Stream.concat(Stream.of(firstLine), lines);

Which is the cleanest solution in my opinion. Note that this is not the same as Java 9’s dropWhile, which would drop more than one line if they match.

Answered By - Holger
Answer Checked By - Robin (JavaFixing Admin)