Java regex - get specific part of string

Question

I'm trying to access a certain part of multiple strings that follow a pattern.

Here's an example of what I'm trying to do.

String s = "Hello my name is Joe";    
if(Pattern.matches(s,"Hello my name is ([\\w]*)"))
{
    System.out.println("Name entered: $1");
}

However, my code never enters inside the "if-statement"

Answer 1

Swap the parameters to the matches method, and your if will work (regex is the 1st parameter, not the second).

However, you still won't print the first capturing group with $1. To do so:

String s = "Hello my name is Joe";    
Matcher m = Pattern.compile("Hello my name is ([\\w]*)").matcher(s);
if(m.matches())
{
    System.out.println("Name entered: " + m.group(1));
}

Answer 2

I think that you are looking for this:

final String s = "Hello my name is Joe";
final Pattern p = Pattern.compile("Hello my name is (\\w++)");
final Matcher m = p.matcher(s);
if (m.matches()) {
   System.out.printf("Name entered: %s\n", m.group(1));
}

This will capture the \w++ group value, only if p matches the entire content of the String. I've replaced \w* with \w++ to exclude zero length matches and eliminate backtracks.

For further reference take a look at The Java Tutorial > Essential Classes - Lesson: Regular Expressions.