java.util.regex.PatternSyntaxException: Dangling meta character ‘+’ near index 0 +

There are reserved character in Regex and you should scape these character to achieve what you want. For example, you can’t use String.split("+"), you have to use String.split("\\+").

The correct operators would be:

String[] operators = new String[] {"-","\\+","https://stackoverflow.com/","\\*","x","\\^","X"};