How to find out if a certain character in a String is Uppercase

I checked all other stackoverflow links about my question but the answers there did not work. So I am asking a similar question with the hope of getting a different answer. This is the code from a class:

public String pozisyonHazirla(String param) {

        String oynananHamle = param;   

        for (int n = 0; n < oynananHamle.length(); n++) {
            if (oynananHamle.substring(n, 1).matches("[0-9]") || oynananHamle.substring(n, 1).matches(".")) {

                String donothing="";

            } else if (oynananHamle.substring(n, 1) == oynananHamle.substring(n, 1).toUpperCase()) {

             sonuc = "Figür Hamlesi Yapıldı";
                break;

            } else {

                sonuc = "Piyon hamlesi yapıldı";
            break;
            }

                         }

            return sonuc;  
        }

The question is that this section of the code is not working and in 100% of the cases the iteration returns the else result which is the assigned value to the sonuc variable.

 } else if (oynananHamle.substring(n, 1) == oynananHamle.substring(n, 1).toUpperCase()) {

             sonuc = "Figür Hamlesi Yapıldı";
                break;

My second question without opening another thread is that in the first case there is a section where I want nothing to be done if the "if" statement is viable so I put something like " String donothing ="";" . Is there anyway to improve this piece of code? Thank you in advanace for your answers and comments...