Matcher throws IllegalStateException after accessing group
I'm trying to write simple command parser class for my project. Here's what I have:
Main.java
public static void main(String[] args) {
CmdParser p = new CmdParser(args);
String st = p.getSourceType();
}
CmdParser.java
import java.util.ArrayList;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class CmdParser {
private String[] args;
public CmdParser(String[] args) {
this.args = args;
}
public String getSourceType() throws ParseException {
ArrayList<String> sourceTypes = new ArrayList<String>();
Pattern p = Pattern.compile("--source-type=([^s]+)");
for (String s : args) {
Matcher m = p.matcher(s);
if (m.groupCount() == 1) {
sourceTypes.add(m.group(1)); //line 28
}
}
return sourceTypes.get(0);
}
}
Running this with java Main --source-type=test causes the following output:
Exception in thread "main" java.lang.IllegalStateException: No match found
at java.util.regex.Matcher.group(Matcher.java:536)
at CmdParser.getSourceType(CmdParser.java:28)
at Main.main(Main.java:11)
I commented line 28 above. How is that possible that even though groupCount is 1, so that should be a correct group index, java throws IllegalStateException in this case? Also, why is pattern not found?
You need to use:
if (m.find() && m.groupCount() == 1) {
sourceTypes.add(m.group(1)); //line 28
}
ie call find or matches before group() method.
你必须在m.group()之前调用m.find() m.group() ：
for (String s : args) {
Matcher m = p.matcher(s);
if (m.find()) {
sourceTypes.add(m.group(1)); //line 28
}
}