/* package whatever; // don't place package name! */
 
import java.util.*;
import java.util.regex.*;
import java.lang.*;
import java.io.*;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		Pattern p = Pattern.compile("^(dog)(?:.+(cat))?");
		for (String s : new String[] {"dog, cat", "dog, dog, cat", "dog, dog, dog", "dog, dog, cat, blah"}) {
			Matcher m = p.matcher(s);
			if (m.find()) {
				System.out.println(m.group(1)+" "+m.group(2));
			}
		}
	}
}

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