Remove a character from every item of a list in JAVA

Erik Steiner :

I have a string like this "-FOREST&-JUNGLE&DESERT"
This string is split up into words in a list like so: [-FOREST, -JUNGLE ,DESERT]
List<String> pattern = Arrays.asList(s.split("\\s*&\\s*"));

Every word with a minus at the beginning must be in one new list and every word without in another like so:

List<String> allowedtags = pattern
                            .stream()
                            .filter(name -> !name.startsWith("-"))
                            .collect(Collectors.toList());

List<String> unwantedtags = pattern
                            .stream()
                            .filter(name -> name.startsWith("-"))
                            .collect(Collectors.toList());

My problem is that my unwantedtags keeps words with a minus at the beginning, but for all my operations I need to get rid of it. If I do the example below, it will not work if "FOREST" is in taglist as my unwantedtags contains "-FOREST".

if (taglist.stream().anyMatch(unwantedtags::contains)) {
                        return !IsWhitelist;
                        }

So how can I fix my unwantedtags list? Maybe in java 8 stream api? Moreover I have the feeling that on the one hand it is working fine to that point, but on the other hand I get the feeling that this is a lot of code for getting just two lists. Can it be optimized?

Ted Hopp :

You can map each element to strip out the leading minus sign after it has been detected:

List<String> unwantedtags = pattern
                            .stream()
                            .filter(name -> name.startsWith("-"))
                            .map(name -> name.substring(1))
                            .collect(Collectors.toList());

The code can be made more efficient by constructing and populating the lists explicitly. Then you can process pattern in a single pass instead of two:

List<String> allowedtags = new ArrayList();
List<String> unwantedtags = new ArrayList();
pattern.stream()
       .forEach(name -> {
                if (name.startsWith("-")) unwantedtags.add(name.substring(1));
                else allowedtags.add(name);
            }
        );