Take input from mouse and keyboard at the same time in Java GUI

You do not have to "add something in loop". You just have to add MouseListener and KeyListener to your GUI element (e.g. Frame) and implement the callback methods as you want.

Take a look, at Toolkit.addAWTEventLstener

This will allow you monitor all the events flowing the event queue.

The problem your going to have is identifying the components that are in the area of effect and overcoming the default behaviour of the components (pressing enter while a text field has focus will trigger a action event on it, but now you want to do something else)

To get the behavior of responding to a mouse over the button and enter being pressed I would:

• Use Key Bindings attached to the JButton to allow it to respond to the enter key.
• Make sure that when doing the above use the InputMap that is associated with the JComponent.WHEN_IN_FOCUSED_WINDOW constant so that the button doesn't actually have to have focus to respond but needs to be in the focused window.
• Of course bind to the KeyStroke associated with KeyEvent.VK_ENTER.
• In the key bindings action, check if the button's model is in the rollOver state by calling isRollOver() on the model.
• and if so, respond.
• Note that none of this above requires a MouseListener because I'm using the ButtonModel's isRollOver in place of that.

As an example, my SSCCE:

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;

import javax.swing.*;

public class MouseKeyResponse extends JPanel {
   private JButton button = new JButton("Button");

   public MouseKeyResponse() {
      button.addActionListener(new ActionListener() {

         @Override
         public void actionPerformed(ActionEvent e) {
            System.out.println("button clicked");
         }
      });
      add(button);

      setUpKeyBindings(button);
   }

   private void setUpKeyBindings(JComponent component) {
      int condition = JComponent.WHEN_IN_FOCUSED_WINDOW;
      InputMap inputMap = component.getInputMap(condition);
      ActionMap actionMap = component.getActionMap();

      String enter = "enter";
      inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_ENTER, 0), enter);
      actionMap.put(enter, new EnterAction());
   }

   private class EnterAction extends AbstractAction {
      @Override
      public void actionPerformed(ActionEvent evt) {
         if (button.isEnabled() && button.getModel().isRollover()) {
            System.out.println("Enter pressed while button rolled over");
            button.doClick();
         }
      }
   }

   private static void createAndShowGui() {
      MouseKeyResponse mainPanel = new MouseKeyResponse();

      JFrame frame = new JFrame("MouseKeyResponse");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}