Use of Robot Class (This sample code will show the use of Robot class to handle the keyboard events. If you run this code and open a notepad then this code will write hi budy in the notepad)

Java.awt.Robot class is used to take the control of mouse and keyboard. Once you get the control, you can do any type of operation related to mouse and keyboard through your java code. This class is used generally for test automation. 

As we can handle windows based Modal dialog and file dialogs.

Sample Code :-

import java.awt.AWTException;
import java.awt.Robot;
import java.awt.event.KeyEvent;

public class RobotExp {
public static void main(String[] args) {
try {
Robot robot = new Robot();
// Creates the delay of 8 sec so that you can open notepad before or we can call notepad from java

// Robot start writing
robot.delay(5000);
robot.keyPress(KeyEvent.VK_H);
robot.keyPress(KeyEvent.VK_I);
robot.keyPress(KeyEvent.VK_SPACE);
robot.keyPress(KeyEvent.VK_B);
robot.keyPress(KeyEvent.VK_U);
robot.keyPress(KeyEvent.VK_D);
robot.keyPress(KeyEvent.VK_Y);

} catch (AWTException e) {
e.printStackTrace();
}
}
} 

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Send Ctrl + Z

robot.keyPress(KeyEvent.VK_CONTROL)
robot.keyPress(KeyEvent.VK_Z)
// CTRL+Z is now pressed (receiving application should see a "key down" event.)
robot.keyRelease(KeyEvent.VK_Z)
robot.keyRelease(KeyEvent.VK_CONTROL)
// CTRL+Z is now released (receiving application should now see a "key up" 

event - as well as a "key pressed" event).

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Use of TAB

    robot.keyPress(KeyEvent.VK_TAB);
    robot.delay(100);
    robot.keyRelease(KeyEvent.VK_TAB);


BY Using all above methods and robot class we can authenticate Windows login modal.