Question

I’m trying to print out a pattern from a string.

String stringToProcess = "Test Test Hello World Test Test";
String pattern = "Hello\\sWorld";
System.out.println(stringToProcess.substring(stringToProcess.indexOf(pattern), stringToProcess.lastIndexOf(pattern)));

When I run this code it seems to give lots of errors depending on how I try to change it and repair it. As it is above, it gives the error:

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: -1

Please note: I already am aware of the Pattern.compile(regex, Pattern); way of doing this. I would like to do it in a different way.

Answer 1

Here is your requested example:

    String stringToProcess = "Test Test Hello World Test Test";
    String patternString = "Hello\\sWorld";
    Pattern pattern = Pattern.compile(patternString);
    Matcher matcher = pattern.matcher(stringToProcess);
    if (matcher.find()) {
        int start = matcher.start();
        int end = matcher.end();
        System.out.println(stringToProcess.substring(start, end));
    }

Beacause you really wanted to use \\s instead of a blank, it will also match Hello\tWorld, Hello\nWorld and all other possible single whitespace character between Hello and World.

The way I have it written it will only print the first found match (if there is one), if you want of print all matches to your pattern replace if with while.

But I wouldn’t use start(), end() and substring() if I didn’t have to, you can just print matcher.group() if you want to print your match.