How to send keystroke to inactive window?

Question

I need to know how to send a keystroke to an inactive window.
Right now i can use the Robot class and send key strokes to the active window but I need to be able to send it to an inactive window.

Answer 1

if you just want to send keys to another java app, this is a kludge hack, windows only
run frame1 and frame2 as separate apps, have them both visible on the screen, focus on frame1.
click the button to send 'enter' to frame2, which will (should) display the JOptionPane
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class Frame1
  public void buildGUI()
    JButton btn = new JButton("Send Enter");
    JFrame f = new JFrame("Frame1");
    f.getContentPane().add(btn);
    f.setBounds(300,100,400,300);
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.setVisible(true);
    btn.addActionListener(new ActionListener(){
      public void actionPerformed(ActionEvent ae){
        sendEnterToFrame2();
  public void sendEnterToFrame2()
    try
      java.io.File file = new java.io.File("ActivateFrame2.vbs");
      java.io.FileWriter fw = new java.io.FileWriter(file);
      fw.write("set ws = WScript.CreateObject(\"WScript.Shell\")\r\nws.AppActivate \"Frame2\" \r\n set ws = nothing");
      fw.close();
      Runtime.getRuntime().exec("WScript.exe ActivateFrame2.vbs");
      file.deleteOnExit();
      Robot robot = new Robot();
      robot.delay(1000);
      robot.keyPress(KeyEvent.VK_ENTER);
      robot.keyRelease(KeyEvent.VK_ENTER);
    catch(Exception e){e.printStackTrace();}
  public static void main(String[] args)
    SwingUtilities.invokeLater(new Runnable(){
      public void run(){
        new Frame1().buildGUI();
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class Frame2
  public void buildGUI()
    JButton btn = new JButton("OK");
    JFrame f = new JFrame("Frame2");
    f.getContentPane().add(btn);
    f.setBounds(700,100,400,300);
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.getRootPane().setDefaultButton(btn);
    f.setVisible(true);
    btn.addActionListener(new ActionListener(){
      public void actionPerformed(ActionEvent ae){
        JOptionPane.showMessageDialog(null,"OK");
  public static void main(String[] args)
    SwingUtilities.invokeLater(new Runnable(){
      public void run(){
        new Frame2().buildGUI();
}