InputValidater.java

class TextVerifier extends InputVerifier {

    private Pattern patternString;
    private Pattern patternInteger;

    public TextVerifier() {
    }

    @Override
    public boolean verify(JComponent input) {

        String name = input.getName();
        patternString = Pattern.compile("^[A-Za-z, ]++$");  //to validate just strings
        patternInteger = Pattern.compile("\\d+"); //to validate just integers

        if (name.equals("txtName") || name.equals("txtSurname")) {
            String text = ((JTextField) input).getText().trim();
            if (!patternString.matcher(text).matches() || text.isEmpty()) {
                return false;
            }

        }

        if (name.equals("txtFirstScore") || name.equals("txtSecondScore") || name.equals("txtThirthScore")) {
            String text = ((JTextField) input).getText();
            if (!patternInteger.matcher(text).matches() || text.isEmpty()) {
                return false;
            }

            int score = Integer.parseInt(((JTextField) input).getText());
            if (score > 100 || score < 0) {
                return false;
            }
        }

        if (name.equals("txtSkill") || name.equals("txtAbsence") || name.equals("txtHomework")) {
            String text = ((JTextField) input).getText();
            if (!patternInteger.matcher(text).matches() ||text.isEmpty()) {
                return false;
            }

            int score = Integer.parseInt(((JTextField) input).getText());
            if (score > 5 || score < 0) {
                return false;
            }
        }

        return true;
    }

}