You can also match case insensitive regexs and make it more readable by using the Pattern.CASE_INSENSITIVE constant like:

Pattern mypattern = Pattern.compile(MYREGEX, Pattern.CASE_INSENSITIVE);
Matcher mymatcher= mypattern.matcher(mystring);

I wouldn't use RegEx for everything.

for(String str : ar)
{
    if(!str.toUpperCase().startsWith("KB"))
        System.out.println(str);
}

@Chaklader

Pattern.CASE_INSENSITIVE is the method I'm known to. It should work. for ASCII only case-insensitive matching

Pattern p = Pattern.compile("YOUR_REGEX GOES HERE", Pattern.CASE_INSENSITIVE);

or for Unicode case-folding matching

Pattern p = Pattern.compile("YOUR_REGEX GOES HERE", Pattern.CASE_INSENSITIVE | Pattern.UNICODE_CASE);

String.matches requires the entire string to match the pattern. As if the pattern has an implied "^...$".

Pattern ignore = Pattern.compile(".*" + Pattern.quote(prompt) + ".*",
    Pattern.CASE_INSENSITIVE);

is for a find like match.

This could have been done with the original pattern as:

if (mIgn.find()) {
    System.out.println("Found at position " + mIgn.start());
}