Java: regular expression replacement

I have this string:

foo bar 567 baz

Now I want to add string num:. Before each number So the result must be:

foo bar num:567 baz

This must also work:

foo 73761 barbazboom!! 87
result:
foo num:73761 barbazboom!! num:87

The regular expression for the search number is: [0-9], but I want to replace the matching substring with num: [matching substring]

Now I've written an example in numbers, but another example can be: add e-mail before each e-mail address:

Solution

Use grouping You can define a group using parentheses (and) and identify the group in the result by $n, where n is the group index

String string = "foo bar 567 baz";
String replaced = string.replaceAll("(\\d+)","num:$1");