Reactions on KeyEvents

private void addKeyListener() {
        this.addKeyListener(
            new KeyListener() {
                @Override
                public void keyTyped(KeyEvent e) {}

                @Override
                public void keyPressed(KeyEvent e) {
                    if ((e.getKeyCode() > 47 && e.getKeyCode() < 58) || e.getKeyCode() == 42 || e.getKeyCode() == 43 || e.getKeyCode() == 45 || e.getKeyCode() == 46 || e.getKeyCode() == 47) {
                        inputField.setText(inputField.getText() + String.valueOf(e.getKeyChar()));
                    }
                    if (e.getKeyCode() == KeyEvent.VK_BACK_SPACE) {
                        inputField.setText(inputField.getText().substring(0, inputField.getText().length() - 1));
                    }
                    if (e.getKeyCode() == KeyEvent.VK_ENTER) {
                        calculate.doClick();
                    }
                    if (e.getKeyCode() == KeyEvent.VK_DELETE) {
                        inputField.setText("");
                    }
                }

                @Override
                public void keyReleased(KeyEvent e) {}
            }
        );
    }