Category: Programming technique
Details:Regular Expressions are a powerful way to match parts of a section of text. Matching a section of text in a group with a repetition operator match expressions as expected, will only remember the
last matched value.
An example in Java:
Matcher m = Pattern.matches("([a-z])+", "abc");
if (m.matches())
for (int i = 1; i < m.groupCount(); i++)
System.out.println("Found: " + m.group(i));
When executed, the above will produce the following:
Found: c
Not exactly what I had in mind. When you retrieve group 1 after evaluation, you will get "a". Even though the pattern matches successfully, the "a" match is overwritten by "b", which is overwritten by "c".
To get the desired result, use the following instead (changes in
red, and note the subtraction of the '+' after the group):
Matcher m = Pattern.matches("\G([a-z])", "abc");
while (m.find())
for (int i = 1; i < m.groupCount(); i++)
System.out.println("Found: " + m.group(i));
This should now produce the following:
Found: a
Found: b
Found: c
Where I learned it:While attempting to extract parts of a date expression in a project I'm working on.
References:
