Comparing Strings in Java .equals()

Question

I'm trying to filter the user's input to make sure its a max of 4 digits and it's not an empty string. Whether I leave it blank or I enter a number, !strInput.equals(null) still comes up true. Am I comparing the string incorrectly?

I also tried: !strInput.equals("") , strInput != null , and strInput != "" though I think it should be .equals(...) since I'm trying to compare values.

        private void updateFast() {
            String strInput = JOptionPane.showInputDialog(null, "How many?");

            if (!strInput.equals(null) && strInput.matches("\\d{0,4}"))
            {
                //do something
            }
            else
            {
                JOptionPane.showMessageDialog(null, "Error. Please Re-enter");
                updateFast();
            }

        }

Answer 1

Change the line:

if (!strInput.equals(null) && strInput.matches("\\d{0,4}"))

To:

if (strInput != null && strInput.matches("\\d{1,4}"))

No need to check if String is empty, the regex checks that.