Allowing the "Enter" key to press the submit button, as opposed to only using MouseClick

There is a simple trick for this. After you constructed the frame with all it buttons do this:

frame.getRootPane().setDefaultButton(submitButton);

For each frame, you can set a default button that will automatically listen to the Enter key (and maybe some other event's I'm not aware of). When you hit enter in that frame, the ActionListeners their actionPerformed() method will be invoked.

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And the problem with your code as far as I see is that your dialog pops up every time you hit a key, because you didn't put it in the if-body. Try changing it to this:

@Override
public void keyPressed(KeyEvent e) {
    if (e.getKeyCode()==KeyEvent.VK_ENTER){
        System.out.println("Hello");

        JOptionPane.showMessageDialog(null , "You've Submitted the name " + nameInput.getText());
    }

}

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UPDATE: I found what is wrong with your code. You are adding the key listener to the Submit button instead of to the TextField. Change your code to this:

SubmitButton listener = new SubmitButton(textBoxToEnterName);
textBoxToEnterName.addActionListener(listener);
submit.addKeyListener(listener);

You can use the top level containers root pane to set a default button, which will allow it to respond to the enter.

SwingUtilities.getRootPane(submitButton).setDefaultButton(submitButton);

This, of course, assumes you've added the button to a valid container ;)

UPDATED

This is a basic example using the JRootPane#setDefaultButton and key bindings API

public class DefaultButton {

    public static void main(String[] args) {
        new DefaultButton();
    }

    public DefaultButton() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame("Test");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }

        });
    }

    public class TestPane extends JPanel {

        private JButton button;
        private JLabel label;
        private int count;

        public TestPane() {

            label = new JLabel("Press the button");
            button = new JButton("Press me");

            setLayout(new GridBagLayout());
            GridBagConstraints gbc = new GridBagConstraints();
            gbc.gridy = 0;
            add(label, gbc);
            gbc.gridy++;
            add(button, gbc);
            gbc.gridy++;
            add(new JButton("No Action Here"), gbc);

            button.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    doButtonPressed(e);
                }

            });

            InputMap im = button.getInputMap(WHEN_ANCESTOR_OF_FOCUSED_COMPONENT);
            ActionMap am = button.getActionMap();

            im.put(KeyStroke.getKeyStroke(KeyEvent.VK_SPACE, 0), "spaced");
            am.put("spaced", new AbstractAction() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    doButtonPressed(e);
                }

            });

        }

        @Override
        public void addNotify() {
            super.addNotify();
            SwingUtilities.getRootPane(button).setDefaultButton(button);
        }

        protected void doButtonPressed(ActionEvent evt) {
            count++;
            label.setText("Pressed " + count + " times");
        }

    }

}

This of course, assumes that the component with focus does not consume the key event in question (like the second button consuming the space or enter keys

In the ActionListener Class you can simply add

public void actionPerformed(ActionEvent event) {
    if (event.getSource()==textField){
        textButton.doClick();
    }
    else if (event.getSource()==textButton) {
        //do something
    }
}