import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Replace_First {

    public static void main(String args[]) {
        Pattern pattern = Pattern.compile("(k|K)ava");
        String text = "kavaSun's regex library Kava is now kava";
        System.out.println("Text before replacing first subsequence is:-" + text);
        Matcher matcher = pattern.matcher(text);
        String str = matcher.replaceFirst("Java");
        System.out.println("Text after replacing first subsequence is:-" + str);
    }
}