Replace special character with an escape preceded special character in Java

Question

In my java code, if a string input has got any of the special characters mentioned, that should get preceded by \\

Special character set is {+, -, &&, ||, !, (, ), {, },[, ], ^, "", ~, *, ?, :, \}. I tried using String.replaceAll(old,new) but to my surprise its not working, even though I am giving proper values for 'old' and 'new'.

if old=":",new="\:"

I put the special chars in a String array, iterated it in a for loop, checked whether it is present in the string, if yes, input.replaceAll(":","\\:"). But its not giving me the intended output. Please help

String[] arr = { "+", "-", "&&", "||", "!", "(", ")", "{", "}",
                "[", "]", "^", "\"", "~", "*", "?", ":", "\\", "AND", "OR" };

    for (int i = 0; i < arr.length; i++) {
//'search' is my input string

        if (search.contains((String) arr[i])) {

            String oldString = (String) arr[i];

            String newString = new String("\\" + arr[i]);
            search = search.replaceAll(oldString, newString);
            String newSearch = new String(search.replaceAll(arr[i],
                    newString));


        }
    }

Answer 1

Once you realise replaceAll takes a regex, it's just a matter of coding your chars as a regex.

Try this:

String newSearch = search.replaceAll("(?=[]\\[+&|!(){}^\"~*?:\\\\-])", "\\\\");

That whacky regex is a "look ahead" - a non capturing assertion that the following char match something - in this case a character class.

Notice how you don't need to escape chars in a character class, except a ] (even the minus don't need escaping if first or last).

The \\\\ is how you code a regex literal \ (escape once for java, once for regex)

Here's a test of this working:

public static void main(String[] args) {
    String search = "code:xy";
    String newSearch = search.replaceAll("(?=[]\\[+&|!(){}^\"~*?:\\\\-])", "\\\\");
    System.out.println(newSearch);
}

Output:

code\:xy

Answer 2

String#replaceAll takes a regex as first parameter. So, your code will fail if the input in the string is a meta-character like - +.

You should use String#replace.

And also you don't need the last assignment: -

String newSearch = new String(search.replaceAll(arr[i], newString));

As, you are not using it at all. You are in fact assigning the modified string back to search, so it's not required.

Also, rather than using new String(...), to build your new string. In fact, you just need a single line in your if-statement.

Ok now, after that explanation, you can now use the below for-loop: -

for (int i = 0; i < arr.length; i++) {
    if (search.contains(arr[i])) {
        search = search.replace(arr[i], "\\" + arr[i]);
    }
}

Answer 3

Try to use the below one. Please use replace method instead of ReplaceAll

search = search.replace(oldString, newString);