Find the last match with Java regex matcher

Question

I\'m trying to get the last result of a match without having to cycle through .find()

Here\'s my code:

String in = \"num 123 num 1 num 698 num 19238          


        

Answer 1

Compared to the currently accepted answer, this one does not blindly discard elements of the list using the".*" prefix. Instead, it uses "(element delimiter)*(element)" to pick out the last element using .group(2). See the function magic_last in code below.

To demonstrate the benefit of this approach I have also included a function to pick out the n-th element which is robust enough to accept a list that has fewer than n elements. See the function magic in code below.

Filtering out the "num " text and only getting the number is left as an exercise for the reader (just add an extra group around the digits pattern: ([0-9]+) and pick out group 4 instead of group 2).

package com.example;

import static java.lang.System.out;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Foo {

  public static void main (String [] args) {
    String element = "num [0-9]+";
    String delimiter = ", ";
    String input;
    input = "here is a num bro: num 001; hope you like it";
    magic_last(input, element, delimiter);
    magic(1, input, element, delimiter);
    magic(2, input, element, delimiter);
    magic(3, input, element, delimiter);
    input = "here are some nums bro: num 001, num 002, num 003, num 004, num 005, num 006; hope you like them";
    magic_last(input, element, delimiter);
    magic(1, input, element, delimiter);
    magic(2, input, element, delimiter);
    magic(3, input, element, delimiter);
    magic(4, input, element, delimiter);
    magic(5, input, element, delimiter);
    magic(6, input, element, delimiter);
    magic(7, input, element, delimiter);
    magic(8, input, element, delimiter);
  }

  public static void magic_last (String input, String element, String delimiter) {
    String regexp = "(" + element + delimiter + ")*(" + element + ")";
    Pattern pattern = Pattern.compile(regexp);
    Matcher matcher = pattern.matcher(input);
    if (matcher.find()) {
        out.println(matcher.group(2));
    }
  }

  public static void magic (int n, String input, String element, String delimiter) {
    String regexp = "(" + element + delimiter + "){0," + (n - 1) + "}(" + element + ")(" + delimiter + element + ")*";
    Pattern pattern = Pattern.compile(regexp);
    Matcher matcher = pattern.matcher(input);
    if (matcher.find()) {
        out.println(matcher.group(2));
    }
  }

}

Output:

num 001
num 001
num 001
num 001
num 006
num 001
num 002
num 003
num 004
num 005
num 006
num 006
num 006