Question

I’m bit confused with Java doc about Matcher in the definition of start() and end().

Matcher.start()

Matcher.end()

Consider the following code:

public static void test()
{
    String candidate = "stackoverflow";
    Pattern p = Pattern.compile("s");
    Matcher m = p.matcher(candidate);
    
    m.find();
    int index = m.start();
    out.println("Index from Match\t"+index);
    
    int offset = m.end();
    out.println("Offset from match\t"+offset);
}

The above will return the following result.

Index from Match 0

Offset from match 1

As I learned every char array or string will start by Index 0 and it’s right in the above expression.
But Offset also returns the same character ‘s’ but why it starts with 1?

Answer 1

No, it doesn’t start with 1 – it starts with 0. The documentation makes it reasonably clear:

Returns the offset after the last character matched.

(Emphasis mine.)

Basically it’s the end of the match in exclusive form, which is common in Java. It means you can do something like:

String text = candidate.substring(matcher.start(), matcher.end());

Note that your “index” and “offset” should really be regarded as “start” and “end” (hence the method names). The terms “index” and “offset” are effectively synonymous in this context; the important point is that start() returns the index/offset of the start of the match, and end() returns the index/offset after the end of the match.