Find substring between two strings

Question

I have a string such as:
file = "UserTemplate324.txt"

I'd like to extract "324". How can I do this without any external libraries like Apache StringUtils?

Well are there going to be files with different names? Because if you only want the 324 of this file alone, that's easy — DreadHeadedDeveloper, Oct 12 '14 at 22:39
I would [for-each](http://stackoverflow.com/a/2451660/2891426) through the String, and if the current character is OK, I'd copy them into a Char Array. After the `for-each`, I'd build the new String from the Array. — Nagy Vilmos, Oct 12 '14 at 22:40

Bohemian · Answer 1 · 2014-10-12T23:05:02.727

3

Assuming you want "the digits just before the dot":

String number = str.replaceAll(".*?(\\d+)\\..*", "$1");

This uses regex to find and capture the digits and replace the entire input with them.

Of minor note is the use of a non-greedy quantifier to consume the minimum leading input (so as not to consume the leading part of the numbers too).

edited Oct 12 '14 at 23:05

answered Oct 12 '14 at 22:40

Bohemian

Thanks, but when I try this, it says "Invalid escape sequence..." – Adam_G Oct 12 '14 at 22:51
@assylias is quite right. I've added the extra backslash. – Bohemian Oct 12 '14 at 23:06

score 2 · Accepted Answer · answered Oct 12 '14 at 22:56

2

If you want to exclude the non-digit characters:

String number = file.replaceAll("\\D+", "");

\\D+ means a series of one or more non digit (0-9) characters and you replace any such series by "" i.e. nothing, which leaves the digits only.

answered Oct 12 '14 at 22:56

assylias

That'll do it. Thank you. Could you explain the first part? – Adam_G Oct 12 '14 at 22:59
1

This is a good simple solution (+1), and I would use it if it suits your file names, but just note that if the input is `"foo123bar456.txt"` the result will be `"123456"` (not `"456"`) – Bohemian Oct 12 '14 at 23:16

2 Answers2