Using Java 8 Streams replace Characters in a String if found in a list of Characters

Assuming

String input;
List<Character> forbidden;

your can use

String result = input.replaceAll(
     forbidden.stream()
              .map(String::valueOf).map‌​(Pattern::quote)
              .collect(Collectors.joining("|")),
     " ");

It converts each forbidden Character to a String using String.valueOf(…), then uses Pattern.quote(…) to convert them to a quoted pattern string, which ensures that the characters are not interpreted as special regex constructs, then all are joined using | which means “or” in a regex pattern. Then, String.replaceAll(regex, replacement) does the actual job.

An alternative without regex (“pure stream operation”) would be

String result = input.chars()
    .map(c -> forbidden.contains((char)c)? ' ': c)
    .collect(StringBuilder::new, (sb, c) -> sb.append((char)c), StringBuilder::append)
    .toString();

This straight-forwardly iterates over all characters, checks whether they are contained in the forbidden collection and replaces them with a space if they are, and finally collects the mapped characters to a new String. It would be more efficient when forbidden gets changed to a Set<Character> rather than List<Character> due to the time complexity of contains, which is invoked for every character.