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javastringjava-stream

Problem while using Collectors.joining() in Java 8 Stream

I tried to filter a stream of characters based on some constraints and then tried to collect them in a string.

This is what I tried:

String s = str.chars()
          .mapToObj(c -> (char) c) 
          .map(Character::toLowerCase)
          .filter(c -> !Character.isWhitespace(c))
          .collect(Collectors.joining());

Collectors.joining() should concatenate the contents of the stream into a String, but this last bit of code produces an error. Why is this happening?

Solution

  • You need to convert the Character to String before joining, you need this:

    ...
.map(c -> Character.toString(c))
.collect(Collectors.joining());