B"H I am unable to extract a consecutive set of numbers from within a (single line) string using ([0-9]+). However, surrounding it with match-all other does work (.*?[0-9].*). Can someone explain to me why ([0-9]+) is not working for this task. Here's my code:

public void testMethod(){
    Pattern pat = Pattern.compile("([0-9]+)");
    Matcher matcher = pat.matcher("red fox 11133434 red fox");
    Boolean matches = matcher.matches();
    Assert.assertTrue("find numbers within string", matches);
    Assert.assertEquals("11133434", matcher.group(1));

You are using a capturing group so this works as you expect: (You need to use find):

Pattern pat = Pattern.compile('([0-9]+)');
    Matcher matcher = pat.matcher('red fox 11133434 red fox');
    Boolean matches = matcher.find();

You will notice the debugs are true and 11133434

A good site to test out your regex and break it down it:


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Thanks Eric for answering the question. Just for completeness I am sharing the definition difference between find and matches from the Java docs:

A matcher is created from a pattern by invoking the pattern's matcher method. Once created, a matcher can be used to perform three different kinds of match operations:

  • The matches method attempts to match the entire input sequence against the pattern.
  • The lookingAt method attempts to match the input sequence, starting at the beginning, against the pattern.
  • The find method scans the input sequence looking for the next subsequence that matches the pattern.
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