Java – dangling metacharacter

When I use ", '*', '(' and ')', I always receive errors about hanging metacharacters

I've tried to escape those characters in regular expressions, but I still get errors This is what I have:

"[-\\+\\*/%\\(\\)]"

to update:

Test:

String input = "+";

String vals = new WNScanner(input).getNextToken();    //**********
System.out.println("token: " + vals);
System.out.println(vals.matches("[-+*/%()]"));

From another class:

...

    String expression = input;
    ...

public String getNextToken() {

    String[] token = {""};

    if (expression.length() == 0)
        return "";

    token = expression.split("\\s");
    recentToken = token[0];
    expression = expression.replaceFirst(token[0],"");     //*************
    expression = expression.trim();

    return token[0];


}

*There are exceptions to these lines

Solution

Well, I don't know what you want to achieve there... Especially in this business:

expression = expression.replaceFirst(token[0],"");

If your input string is "", then your entire regular expression is "" This is illegal

You need to reference the input string to use it in any regular expression - related operation, including string Replacefirst() and Replaceall() (excluding. Replace()...)

Therefore, do the following:

final String re = Pattern.quote(token[0]);
expression = expression.replaceFirst(re,"");