Java Language Using capture groups

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If you need to extract a part of string from the input string, we can use capture groups of regex.

For this example, we'll start with a simple phone number regex:


If parentheses are added to the regex, each set of parentheses is considered a capturing group. In this case, we are using what are called numbered capture groups:

^-----^ ^-----^ ^-----^
Group 1 Group 2 Group 3

Before we can use it in Java, we must not forget to follow the rules of Strings, escaping the backslashes, resulting in the following pattern:


We first need to compile the regex pattern to make a Pattern and then we need a Matcher to match our input string with the pattern:

Pattern phonePattern = Pattern.compile("(\\d{3})-(\\d{3})-(\\d{4})");
Matcher phoneMatcher = phonePattern.matcher("abcd800-555-1234wxyz");

Next, the Matcher needs to find the first subsequence that matches the regex:


Now, using the group method, we can extract the data from the string:

String number =; //"800-555-1234" (Group 0 is everything the regex matched)
String aCode =; //"800"
String threeDigit =; //"555"
String fourDigit =; //"1234"

Note: can be used in place of

Java SE 7

Java 7 introduced named capture groups. Named capture groups function the same as numbered capture groups (but with a name instead of a number), although there are slight syntax changes. Using named capture groups improves readability.

We can alter the above code to use named groups:

^----------------^ ^-----^ ^-----^
AreaCode           Group 2 Group 3

To get the contents of "AreaCode", we can instead use:

String aCode ="AreaCode"); //"800"
Using regex with custom behaviour by compiling the Pattern with flags