Hello. I found suspicious condition in implementation of method JrtFileSystem.getPathMatcher(String) https://github.com/openjdk/jdk/blob/master/src/java.base/share/classes/jdk/i... public PathMatcher getPathMatcher(String syntaxAndInput) { int pos = syntaxAndInput.indexOf(':'); if (pos <= 0 || pos == syntaxAndInput.length()) { throw new IllegalArgumentException("pos is " + pos); } Variable pos is a result of String.indexOf(char) call. It is compared with the length() of the same String. This condition 'pos == syntaxAndInput.length()' will always be false: String.indexOf() can't return any value greater than length()-1. Perhaps it was intended to be 'pos == syntaxAndInput.length() - 1'? BTW, I think exception message could be improved. Current message 'pos is -1' is not user friendly. Andrey Turbanov