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
– DreadHeadedDeveloper, Commented Oct 12, 2014 at 22:39
I would for-each 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
– Nagy Vilmos, Commented Oct 12, 2014 at 22:40

Bohemian · Accepted Answer · 2014-10-12 23:05:02Z

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, 2014 at 23:05

answered Oct 12, 2014 at 22:40

Bohemian♦

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2 Comments

Adam_G Over a year ago

Thanks, but when I try this, it says "Invalid escape sequence..."

Bohemian Over a year ago

@assylias is quite right. I've added the extra backslash.

assylias · Accepted Answer · 2014-10-12 22:56:27Z

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, 2014 at 22:56

assylias

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2 Comments

Adam_G Over a year ago

That'll do it. Thank you. Could you explain the first part?

Bohemian Over a year ago

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")

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