Problem replacing words using [^a-zA-Z] regex

String homeworkTitle = "Worksheet%#5_blah";
String unwantedCharactersRegex = "[^a-zA-Z]";
String replacementString = "+";
homeworkTitle = homeworkTitle.replaceAll(unwantedCharactersRegex,replacementString);
System.out.println(homeworkTitle);

[^a-zA-Z]+

String unwantedCharactersRegex = "[^a-zA-Z]"

String unwantedCharactersRegex = "[^a-zA-Z]+"