title: How to make a simple keypad on java to input in JTextFields efficiently?
body: <p>I am working on a keypad on java that will be used to input data in two JTextField (x &amp; y). And Once the user clicks "Enter", It should evaluate the difference of x and y.   Do I have to add bunch of actionListeners for each button?? Is there an efficient way to do it. </p>
  
  <p>So far on my code, I have all the buttons I need, but instead of using my keyboard, I want to use the virtual keypad instead to enter the numbers (technically, a String). Any suggestions? </p>
  
  <pre><code>import javax.swing.*;
  import java.awt.*;
  
  public class EmbeddedMain extends JFrame
  {
  
      public static void main (String[] args)
          {
          EmbeddedMain em = new EmbeddedMain();
          }
  
  
      public EmbeddedMain()
      {
          setTitle("testing");
          setSize(450,350);
          setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          setLocationRelativeTo(null);
          setLayout(new GridLayout(4,5,3,3));
  
      JButton button1= new JButton("7");
      JButton button2= new JButton("8");
      JButton button3= new JButton("9");
      JButton button4= new JButton("4");
      JButton button5= new JButton("5");
      JButton button6= new JButton("6");
      JButton button7= new JButton("1");
      JButton button8= new JButton("2");
      JButton button9= new JButton("3");
      JButton button0= new JButton("0");
      JButton buttonR= new JButton("Reset");
      JButton buttonE= new JButton("Enter");
  
       JTextField x = new JTextField("      ");
       JTextField y = new JTextField("      ");
       JTextField CPP_entry = new JTextField("    ");
  
     CPP_entry.setEditable(false);        
  
      add(button1);
      add(button2);
      add(button3);
      add(new JLabel("    x:")); 
      add(x); 
      add(button4);
      add(button5);
      add(button6);
      add(new JLabel("    y:")); 
      add(y); 
      add(button7);
      add(button8);
      add(button9);
      add(new JLabel("    x-y:")); 
      add(CPP_entry); 
      add(buttonR);
      add(button0);
      add(buttonE);
  
          setVisible(true);
  
  
          }
  
          }
  </code></pre>