Using Regular Expressions to Extract a Value in Java

Tags: regex java
Question!

I have several strings in the rough form:

[some text] [some number] [some more text]

I want to extract the text in [some number] using the Java Regex classes.

I know roughly what regular expression I want to use (though all suggestions are welcome). What I'm really interested in are the Java calls to take the regex string and use it on the source data to produce the value of [some number].

EDIT: I should add that I'm only interested in a single [some number] (basically, the first instance). The source strings are short and I'm not going to be looking for multiple occurrences of [some number].



Answers
Pattern p = Pattern.compile("(\\D+)(\\d+)(.*)");
Matcher m = p.matcher("this is your number:1234 thank you");
if (m.find()) {
    String someNumberStr = m.group(2);
    int someNumberInt = Integer.parseInt(someNumberStr);
}


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

public class Regex1 {
    public static void main(String[]args) {
        Pattern p = Pattern.compile("\\d+");
        Matcher m = p.matcher("hello1234goodboy789very2345");
        while(m.find()) {
            System.out.println(m.group());
        }
    }
}

Output:

1234
789
2345
By : javaMan


Allain basically has the java code, so you can use that. However, his expression only matches if your numbers are only preceded by a stream of word characters.

"(\\d+)"

should be able to find the first string of digits. You don't need to specify what's before it, if you're sure that it's going to be the first string of digits. Likewise, there is no use to specify what's after it, unless you want that. If you just want the number, and are sure that it will be the first string of one or more digits then that's all you need.

If you expect it to be offset by spaces, it will make it even more distinct to specify

"\\s+(\\d+)\\s+"

might be better.

If you need all three parts, this will do:

"(\\D+)(\\d+)(.*)"

EDIT The Expressions given by Allain and Jack suggest that you need to specify some subset of non-digits in order to capture digits. If you tell the regex engine you're looking for \d then it's going to ignore everything before the digits. If J or A's expression fits your pattern, then the whole match equals the input string. And there's no reason to specify it. It probably slows a clean match down, if it isn't totally ignored.

By : Axeman


This video can help you solving your question :)
By: admin