Find a Regex Pattern in a String

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.

The only other way I am aware of is to use Matcher.start() .... but that involves Pattern.compile(regex, Pattern) which you already know. — NawaMan
– NawaMan, Commented Dec 13, 2012 at 7:50
use the Pattern and Matcher and use start() and end() (also your \s should be \\s. — jlordo
– jlordo, Commented Dec 13, 2012 at 7:50
Why don't you just use String pattern = "Hello World";? I.e. you don't need a regex to define a a space symbol. — svz
– svz, Commented Dec 13, 2012 at 7:52

jlordo · Accepted Answer · 2012-12-13 07:59:49Z

0

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.

edited Dec 13, 2012 at 7:59

answered Dec 13, 2012 at 7:54

jlordo

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Comments

neb1 · Accepted Answer · 2012-12-13 08:47:21Z

0

This is function that return the start location of the sentence :

public  static int decodeString(String msg,String sentence) {
        Pattern p = Pattern.compile("(.*)"+sentence+"(.*)");
        Matcher m = p.matcher(msg);
        if (m.matches()) {
           return  m.end(1);
        }
        return -1;
    }

Note that this give the last matching. If we have some matches we need to work with loop

answered Dec 13, 2012 at 8:47

neb1

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