Group matching with Asterisk?
How do I get content for a group with an asterisk?
For example, I would like to get a comma-separated list, e. g 1,2,3,4,5
.
private static final String LIST_REGEX = "^(\\d+)(,\\d+)*$";
private static final Pattern LIST_PATTERN = Pattern.compile(LIST_REGEX);
public static void main(String[] args) {
final String list = "1,2,3,4,5";
final Matcher matcher = LIST_PATTERN.matcher(list);
System.out.println(matcher.matches());
for (int i = 0, n = matcher.groupCount(); i < n; i++) {
System.out.println(i + "\t" + matcher.group(i));
}
}
And the conclusion
true
0 1,2,3,4,5
1 1
How can I get each record i.e. e. 1
, 2
, 3
, ...?
I am looking for a general solution. This is just a demo example.
Imagine a more complex regex, for example ^\\[(\\d+)(,\\d+)*\\]$
to match a list like[1,2,3,4,5]
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You can use String.split()
.
for (String segment : "1,2,3,4,5".split(","))
System.out.println(segment);
Or, you can capture multiple times with the assertion:
Pattern pattern = Pattern.compile("(\\d),?");
for (Matcher m = pattern.matcher("1,2,3,4,5");; m.find())
m.group(1);
For your second example, which you added, you can make a similar match.
for (String segment : "!!!!![1,2,3,4,5] //"
.replaceFirst("^\\D*(\\d(?:,\\d+)*)\\D*$", "$1")
.split(","))
System.out.println(segment);
I made a demo of the online code . Hope this is what you wanted.
how can I get all matches (zero, one or more) for an asterisked arbiter group
(xyz)*
? [The group repeats, and I would like to get every recapture.]
No, you cannot. Regex capture groups and backlinks tell you why:
The return value for this group is the last captured
Since the capture group with a quantifier is kept on its own number, what value does the engine return when checking the group? All motors return the last committed value. For example, if you match a string
A_B_C_D_
with([A-Z]_)+
, then when checking for a match, group 1 will beD_
. With the exception of the .NET engine, all intermediate values are lost. Basically, group 1 is overwritten every time its pattern is matched.
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I assume you can search for something like the following, this will handle both of your examples.
private static final String LIST_REGEX = "^\\[?(\\d+(?:,\\d+)*)\\]?$";
private static final Pattern LIST_PATTERN = Pattern.compile(LIST_REGEX);
public static void main(String[] args) {
final String list = "[1,2,3,4,5]";
final Matcher matcher = LIST_PATTERN.matcher(list);
matcher.find();
int i = 0;
String[] vals = matcher.group(1).split(",");
System.out.println(matcher.matches());
System.out.println(i + "\t" + matcher.group(1));
for (String x : vals) {
i++;
System.out.println(i + "\t" + x);
}
}
Output
true
0 1,2,3,4,5
1 1
2 2
3 3
4 4
5 5
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