Develop Reference

Swing application Thread locked by JNA

I have Swing application on Windows 10. Also I added Low Level Keyboard hook which should intercept keyboard events and remap for example 'z' to 's' button.
This is needed to hook keyboard events outside my java application. I have implemented it using JNA version 5.6.0 and jna-platform version 5.6.0. It works fine but not inside my Swing application.
My problem is when the hook is ON, swing application a kind of locked. I can not press to any Jbutton and even close Jframe at all.
My guess is that it has something to do with threads, but I'm very weak at threads and multithreading.
Reproducible example.
TestFrame class:
import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class TestFrame extends JFrame {
public static void main(String [] args) {
TestFrame frame = new TestFrame();
JTextField textField=new JTextField();
textField.setBounds(50,50, 150,20);
JButton button=new JButton("Click Here");
button.setBounds(50,100,95,30);
button.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
ReMapper reMapper = new ReMapper();
reMapper.reMapOn();
textField.setText("Is my frame locked?");
}
});
frame.add(button);
frame.add(textField);
frame.setSize(400,400);
frame.setLayout(null);
frame.setVisible(true);
}
}
ReMapper class:
import com.sun.jna.Pointer;
import com.sun.jna.platform.win32.*;
public class ReMapper {
private static WinUser.HHOOK hHook;
final User32 user32Library = User32.INSTANCE;
WinDef.HMODULE hMod = Kernel32.INSTANCE.GetModuleHandle(null);
static WinUser.INPUT input = new WinUser.INPUT();
public void reMapOn() {
WinUser.LowLevelKeyboardProc keyboardHook = new WinUser.LowLevelKeyboardProc() {
#Override
public WinDef.LRESULT callback(int nCode, WinDef.WPARAM wParam, WinUser.KBDLLHOOKSTRUCT kbDllHookStruct) {
if (nCode >= 0) {
if (wParam.intValue() == WinUser.WM_KEYDOWN) {
if (kbDllHookStruct.vkCode == 90) { // 90 is key code = z
sendKey(83); // 83 is key code = s
return new WinDef.LRESULT(1);
}
}
}
Pointer ptr = kbDllHookStruct.getPointer();
long peer = Pointer.nativeValue(ptr);
return user32Library.CallNextHookEx(hHook, nCode, wParam, new WinDef.LPARAM(peer));
}
};
hHook = user32Library.SetWindowsHookEx(WinUser.WH_KEYBOARD_LL, keyboardHook, hMod, 0);
int result;
WinUser.MSG msg = new WinUser.MSG();
while ((result = user32Library.GetMessage(msg, null, 0, 0)) != 0) {
if (result == -1) {
break;
} else {
user32Library.TranslateMessage(msg);
user32Library.DispatchMessage(msg);
}
}
}
static void sendKey(int keyCode) {
input.type = new WinDef.DWORD(WinUser.INPUT.INPUT_KEYBOARD);
input.input.setType("ki"); // Because setting INPUT_INPUT_KEYBOARD is not enough: https://groups.google.com/d/msg/jna-users/NDBGwC1VZbU/cjYCQ1CjBwAJ
input.input.ki.wScan = new WinDef.WORD(0);
input.input.ki.time = new WinDef.DWORD(0);
input.input.ki.dwExtraInfo = new BaseTSD.ULONG_PTR(0);
// Press
input.input.ki.wVk = new WinDef.WORD(keyCode); // 0x41
input.input.ki.dwFlags = new WinDef.DWORD(0); // keydown
User32.INSTANCE.SendInput(new WinDef.DWORD(1), (WinUser.INPUT[]) input.toArray(1), input.size());
// Release
input.input.ki.wVk = new WinDef.WORD(keyCode); // 0x41
input.input.ki.dwFlags = new WinDef.DWORD(2); // keyup
User32.INSTANCE.SendInput(new WinDef.DWORD(1), (WinUser.INPUT[]) input.toArray(1), input.size());
}
}
Here is the screen with locked Jframe after clicking 'Click Here' button:
ReMapper class works fine separately from Swing application.
reMapOn() allows to remap 'z' to 's'. But I need it to work inside my Swing app and not block it..
Does anyone know what the problem might be and how to fix it?

Looking at your reMapOn code, it has a while loop and that points to the fact that it could run indefinitely and block the applications UI.
What you need to do is simply in your addActionListener method call the reMapOn method on its own thread. This can be done either using a simple Thread or Swing Worker:
Swing Worker example (preferred solution as you can override done and manipulate swing components if needed in that method when the remapper had ended):
new SwingWorker<Void, Void>() {
#Override
protected Void doInBackground() throws Exception {
ReMapper reMapper = new ReMapper();
reMapper.reMapOn();
return null;
}
}.execute();
textField.setText("Is my frame locked?");
Thread example:
new Thread(() -> {
ReMapper reMapper = new ReMapper();
reMapper.reMapOn();
}).start();
textField.setText("Is my frame locked?");
Some other points are:
Don't use a null/AbsoluteLayout rather use an appropriate LayoutManager
Don't call setBounds() or setSize() on components, if you use a correct layout manager this will be handled for you
Call JFrame#pack() before setting the frame to visible when using a LayoutManager
Dont extend the JFrameclass unnecessarily
All Swing components should be called on the EDT via SwingUtilities.invokeLater

Implementing GUI with Java application

I'm quite the beginner when it comes to java & coding in general, so I apologise for any overly obvious questions asked. I've just completed part of an application which reads data from an SQL database, then sends some stuff to print to socket depending on what information is read. I'm now trying to learn swing and get a GUI working with the application. Currently I have 2 forms, the first is used to select a printer, then the second will (hopefully) work as a log/ console which tells the user what and when stuff is happening. I've got the code and the forms together in a project.
I was wanting to find out how I can make the class which has my code in run when a Jbutton is pressed on a GUI, as well as how I can stop it from running when a different JButton is pressed.
The code from the Swing Form (Form2.java) is as follows:
package com.company;
import javax.swing.*;
public class Form2
{
private JTextArea jtaConsole;
private JPanel Jframer;
private JButton stopButton;
private JButton startButton;
public Form2(String message)
{
JFrame frame = new JFrame("Print Application");
frame.setContentPane(this.Jframer);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setResizable(true);
frame.setVisible(true);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
jtaConsole.append(" Printer selected: " + message + "\n");
}
}
And the code from the class I want the JButton to run is as follows:
package com.company;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.Socket;
import java.sql.*;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
public class ZebraCode
{
public static void main(String[] args)
{
{
while (true)
{
//SQL login.
String connectionString = "jdbc:sqlserver://:;database=;user=;password=!!;";
//Select Data.
String SQL = "SELECT TOP 2 [PK_PrintQueueID],[FK_PrinterID],[FK_BarcodeTypeID],[Barcode],[Quantity],[QueueDate],[ProcessedDate] FROM [Brad].[dbo].[PrintQueue] -- WHERE ProcessedDate IS NULL";
//Connection Variable & Time Settings.
Connection connection = null;
DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
Date date = new Date();
try
{
connection = DriverManager.getConnection(connectionString);
Statement stmt = connection.createStatement();
Statement stmt2 = null;
ResultSet rs = stmt.executeQuery(SQL);
while (rs.next())
{
// Get barcode value to split & Set date.
String FK_BarcodeTypeID = rs.getString("FK_BarcodeTypeID");
String barcode = rs.getString("Barcode");
String[] parts = barcode.split("-");
String part1 = parts[0];
String SQL2 = "UPDATE PrintQueue SET ProcessedDate = '" + dateFormat.format(date) + "' WHERE PK_PrintQueueID = '" + rs.getString("PK_PrintQueueID")+"'";
stmt2 = connection.createStatement();
stmt2.executeUpdate(SQL2);
// Action based on type of barcode.
if (FK_BarcodeTypeID.equals("1"))
{
// Type 128 barcode.
String zpl = "^XA^BY2,3,140^FT80,200^BCN,Y,N,N^FD>:" + rs.getString("Barcode") + "^FS^FT200,250^A0N,42,40^FH^FD" + part1 + "^FS^XZ";
printlabel(zpl);
System.out.println("New serialized barcode added.\nPrinting: " + (rs.getString("Barcode")));
System.out.println("Process date: " + dateFormat.format(date) + ".\n");
}
else
{
// Type 39 barcode.
String zpl = "CT~~CD,~CC^~CT~ ^XA~TA000~JSN^LT0^MNW^MTT^PON^PMN^LH0,0^JMA^PR4,4~SD15^JUS^LRN^CI0^XZ^XA^MMT^PW674^LL0376 ^LS0 ^BY2,3,151^FT84,249^BCN,,Y,N^FD>:" + rs.getString("Barcode") + "^FS ^PQ1,0,1,Y^XZ";
printlabel(zpl);
System.out.println("New un-serialized barcode added.\nPrinting: " + (rs.getString("Barcode")));
System.out.println("Process date: " + dateFormat.format(date) + ".\n");
}
}
} catch (SQLException e)
{
e.printStackTrace();
}
try
{
//Makes execution sleep for 5 seconds.
Thread.sleep(5000);
}
catch (InterruptedException ez)
{
}
}
}
}
//Printer Info.
public static void printlabel(String zpl)
{
try
{
Socket clientSocket;
clientSocket = new Socket("", );
DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());
outToServer.writeBytes(zpl);
clientSocket.close();
}
catch (IOException e)
{
e.printStackTrace();
}
}
}
Any tutorials or direction as to how I can learn this would be appreciated.
Thanks!

You want to add an action listener.. here is an example. Below are two examples on how to do so using lambdas and not using one.
JButton button = new JButton("Click Me!");
// Without lambda
button.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent evt) {
// Code to execture when clicked
}
});
//With lambda
button.addActionListener(e -> {
//code to execute when clicked
});
I'd also advise you to do a little reading, http://www.tutorialspoint.com/design_pattern/mvc_pattern.htm

Your question is a bit broad but let me offer some suggestions:
First off, you really don't want to have a JButton run the database code unchanged as doing this would be shoehorning a linear console program into an event-driven GUI, a recipe for disaster. Note that as written all your database code is held within a single static main method, and so there would be no way for the GUI to be able to control the running of that code. Either it runs or it doesn't, that's it, and no easy way for the database code to return its data to the GUI.
Instead first change that database code so that it is much more modular and OOP-friendly, including creating proper classes with state (instance fields) and behavior (instance methods), and getting almost all that code out of the static main method.
What I'm asking you to do is to create a proper model for your GUI, aka your view. Only after doing this would you have your GUI create a model object and call its methods on button push within your ActionListener. You will also want to call any long-running code within a background thread such as can be obtained with a SwingWorker.
Other issues:
You never initialize your JPanel or JTextArea variables, and so you're both adding a null variable as your JFrame's JPanel and calling methods on a null JTextArea variable, both of which will throw NullPointerExceptions.

Here's a part of code I developed to better understand Java gui. I'm also a begginer.
It's three classes: starter class, ongoing non gui processes, gui with the swingworker method. Simple, works, can safely update a lot of gui components from Swingworkers process method (passes a class instance as argument). Whole code so it can be copy/pasted:
package structure;
public class Starter {
public static void main(String[] args) {
Gui1 thegui = new Gui1();
}
}
LOGIC
package structure;
public class Logical {
String realtimestuff;
public String getRealtimestuff() {
return realtimestuff;
}
public void setRealtimestuff(String realtimestuff) {
this.realtimestuff = realtimestuff;
}
//MAIN LOGICAL PROCESS..
public void process(){
// do important realtime stuff
if (getRealtimestuff()=="one thing"){
setRealtimestuff("another thing");
}else{setRealtimestuff("one thing");
}
// sleep a while for readibility of label in GUI
//System.out.println(getRealtimestuff());
try {
Thread.sleep(250);
} catch (InterruptedException e) {
System.out.println("sleep interrupted");
return;
}
}
}
GUI CLASS with Swingworker
package structure;
import javax.swing.JFrame;
import javax.swing.JPanel;
import java.awt.BorderLayout;
import java.awt.EventQueue;
import javax.swing.JLabel;
import java.util.List;
import javax.swing.*;
public class Gui1 {
final class Dataclass{
String stringtosend;
public Dataclass(String jedan){
//super();
this.stringtosend = jedan;
}
}
// EDT constructor
JFrame frame;
public Gui1(){
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
initialize();
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
public void initialize() {
// JUST A FRAME WITH A PANEL AND A LABEL I WISH TO UPDATE
frame = new JFrame();
frame.setBounds(100, 100, 200, 90);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JPanel panel = new JPanel();
frame.getContentPane().add(panel, BorderLayout.NORTH);
JLabel lblNovaOznaka = new JLabel();
panel.add(lblNovaOznaka);
frame.setVisible(true);
SwingWorker <Void, Dataclass> worker = new SwingWorker <Void, Dataclass>(){
#Override
protected Void doInBackground() throws Exception {
Logical logic = new Logical();
boolean looper = true;
String localstring;
while (looper == true){
logic.process();
localstring = logic.getRealtimestuff();
publish(new Dataclass(localstring));
}
return null;
}
#Override
protected void process(List<Dataclass> klasa) {
// do a lot of things in background and then pass a loto of arguments for gui updates
Dataclass xxx = klasa.get(getProgress());
lblNovaOznaka.setText(xxx.stringtosend);
}
};
worker.execute();
}
}

JFrame doesn't appear with red background

I have strange problem when running my Java program.
It's designed to:
run external app specified in bat file and display fullscreen wallpaper
"hide" wallpaper for some time when buttons combination pressed
warn user that 5sec left so he can save work
when timeout occures display again fullscreen wallpaper and do some other stuff from bats
quit program when button combination pressed
warinng user is realized as displaying fullscreen red box for 200ms
I'm using visible function to do this.
It shows standard fullscreen frame discaring color settings. but only when I comment frame.setUndecorated(true). when uncommented I see only icon in taskbar.
On the other hand when I launch (Using BlueJ) only function visible
the red frame is displayed for specified amount of time. Simply standalone function works perfectly (in my oppinion) even if frame.setUndecorated(true) is used .
what can be wrong that I can't launch that red frame in fullscreen?
olympicApp class:
import java.awt.*;
import java.awt.Color;
import java.awt.event.*;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.Graphics;
import java.awt.image.*;
import java.io.*;
import java.io.IOException;
import javax.imageio.*;
import javax.swing.*;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JComponent;
public class olympicApp extends JComponent {
alertApp alert;
BufferedImage img;
public olympicApp()
{
try
{
img = ImageIO.read(new File("wallpaper.jpg"));
}
catch (IOException e)
{
}
}
public void paint(Graphics g)
{
g.drawImage(img, 0, 0, null);
}
public Dimension getPreferredSize()
{
if (img == null)
{
return new Dimension(200,200);
}
else
{
return new Dimension(img.getWidth(null), img.getHeight(null));
}
}
public static void visible()
{
JFrame frame = new JFrame();
frame.getContentPane().setBackground(Color.red);
frame.setExtendedState(JFrame.MAXIMIZED_BOTH);
frame.dispose();
//frame.setUndecorated(true);
frame.setAlwaysOnTop(true);
frame.pack();
frame.setVisible(true);
try
{
frame.setVisible(true);
Thread.sleep(500);
frame.setVisible(false);
}
catch(Exception ex)
{
}
frame.setAlwaysOnTop(false);
frame.setVisible(false);
}
public static void main(String[] args)
{
//alertApp reminder = new alertApp();
try
{
Process process = Runtime.getRuntime().exec("start-lv.bat");
Thread.sleep(500);
}
catch (IOException | InterruptedException e)
{
}
JFrame f = new JFrame("olympic");
f.setExtendedState(JFrame.MAXIMIZED_BOTH);
f.setUndecorated(true);
f.setAlwaysOnTop(true);
f.addWindowListener(new WindowAdapter()
{
public void windowClosing(WindowEvent e)
{
System.exit(0);
}
});
f.add(new olympicApp());
f.pack();
f.setVisible(true);
f.addKeyListener(new KeyListener()
{
public void keyPressed(KeyEvent kevt)
{
if(kevt.getKeyChar()=='l')
{
if(kevt.isAltDown())
{
f.setAlwaysOnTop(false);
f.setVisible(false);
try
{
Thread.sleep(5*1000);
visible();
Thread.sleep(5*1000);
//Process process = Runtime.getRuntime().exec("saving.bat");
Thread.sleep(500);
f.setAlwaysOnTop(true);
f.setVisible(true);
Process process2 = Runtime.getRuntime().exec("kopia.bat");
}
catch(IOException | InterruptedException e)
{
}
}
}
if(kevt.getKeyChar()=='q')
{
if(kevt.isAltDown())
{
System.exit(0);
}
}
}
public void keyTyped(KeyEvent kevt)
{
}
public void keyReleased(KeyEvent kevt)
{
}
});
}
}

I would imagine that you're going to have to do something in here...
public class alertApp {
public static void main(String[] args) {
// Sample loop to flash every 2 seconds
}
}
This is called when your program starts and where you should put the code to get the program running
I would also strogly recommend that you take a look at Code Conventions for the Java TM Programming Language, it will make it easier for people to read your code and for you to read others
As well as Concurrency in Swing and How to use Swing Timers which will help you solve other potential issues
I put neccessary code in visible funciton. I can see the frame but color information is discarted. Thanks for Concurrency and Timers, but I think the problem isn't connected to thread.sleep()
Then you didn't read the links...
public void keyPressed(KeyEvent kevt) {
if (kevt.getKeyChar() == 'l') {
if (kevt.isAltDown()) {
f.setAlwaysOnTop(false);
f.setVisible(false);
try {
Thread.sleep(5 * 1000);
visible();
Thread.sleep(5 * 1000);
//Process process = Runtime.getRuntime().exec("saving.bat");
Thread.sleep(500);
f.setAlwaysOnTop(true);
f.setVisible(true);
Process process2 = Runtime.getRuntime().exec("kopia.bat");
} catch (IOException | InterruptedException e) {
}
}
}
keyPressed is executed within the context of the Event Dispatching Thread, so when you call Thread.sleep, it prevents the EDT from processing the Event Queue, preventing it from painting or responding to other events

Window JPanel is transparent?

I have a main window with 4 JButtons and an action listener, and three of them call another window and the fourth exits. Two of my windows work fine, but for some reason my window that waits for a client to connect opens and you can see the boundary of the window, but the inside of the window is transparent.
I tried saying new HostWindow() from my main class, and that worked fine; it's just when I call it from my StartWindow class that it doesn't work.
code:
StartWindow:
public class StartWindow extends JFrame{
private JPanel pane;
private JButton host;
private JButton join;
private JButton comp;
private JButton exit;
public StartWindow()
{
this.setSize(220, 110);
this.setTitle("Closed Arena");
pane = new JPanel();
this.add(pane);
host = new JButton("Host Match");
host.addActionListener(new myButtonListener());
join = new JButton("Join Match");
join.addActionListener(new myButtonListener());
comp = new JButton("Play Computer");
comp.addActionListener(new myButtonListener());
exit = new JButton("Exit");
exit.addActionListener(new myButtonListener());
pane.add(host);
pane.add(join);
pane.add(comp);
pane.add(exit);
this.setResizable(false);
pane.setVisible(true);
this.setVisible(true);
this.setDefaultCloseOperation(EXIT_ON_CLOSE);
//If I make a new Hostwindow here it displays properly
//new HostWindow();
}
private class myButtonListener implements ActionListener
{
#Override
public void actionPerformed(ActionEvent e)
{
Object source = e.getSource();
if(source.equals(host))
{
close();
//But here it displays improperly.
new HostWindow();
}
if(source.equals(join))
{
close();
new JoinWindow();
}
if(source.equals(comp))
{
close();
new Arena();
}
if(source.equals(exit))
{
close();
}
}
}
public void close()
{
this.dispose();
}
}
HostWindow:
private JPanel panel;
private JLabel text;
private JButton stop;
private LabelEditor edit;
private Thread editThread;
private ServerSocket server;
private Socket mySocket;
public HostWindow()
{
panel = new JPanel();
text = new JLabel("Waiting for client");
stop = new JButton("Stop");
stop.addActionListener(new buttonList());
panel.add(text);
panel.add(stop);
this.add(panel);
this.setResizable(false);
this.setSize(160, 90);
this.setTitle("Server");
this.setVisible(true);
this.setDefaultCloseOperation(EXIT_ON_CLOSE);
edit = new LabelEditor(text, "Waiting for client", 700);
editThread = new Thread(edit);
editThread.start();
try
{
server = new ServerSocket(4011);
mySocket = server.accept();
server.close();
new Arena(mySocket, true);
}
catch (IOException e) {
System.out.print("Failed to set up server!");
}
editThread.interrupt();
this.dispose();
}
Edit: HostWindow does extend JFrame, I jsut didn't copy-paste the heading, but it looks like this:
public class HostWindow extends JFrame {
Edit2: Thank you answerers, it was fixed when I made it so that the serer starts in a separate thread:
if(source.equals(host))
{
close();
HostWindow hoster = new HostWindow();
Thread hosterThread = new Thread(hoster);
hosterThread.start();
}
and in hostwindow:
I moved the server stuff into the run.
public void run() {
try
{
server = new ServerSocket(4011);
mySocket = server.accept();
server.close();
new Arena(mySocket, true);
}
catch (IOException e) {
System.out.print("Failed to set up server!");
}
editThread.interrupt();
this.dispose();
}

The problem here is that you're performing a long lasting blocking operation inside the UIThread.
Threads are simultanous sequences of commands that run inside a single program (I recommend reading up on Java concurrency ). There is a thread usually refered to as the UIThread that performs drawing of the UI elements and works with their code.
Creating a socket - a connection to a remote host means you're starting a process that can take several seconds to perform. And this is happening inside the constructor of the UI class, inside the UIThread. Until the connection is established the rest of the code in the constructor cannot run. This is because the connection process is a blocking operation - the code after the socket creation won't run until the socket creation is finishsed.
So you should move the socket creation to a different thread.

Firstly, I think your example is incorrect HostWindow doesn't extend from anything, yet you seem to be treating it like a window...
Secondly
try
{
server = new ServerSocket(4011);
mySocket = server.accept();
server.close();
new Arena(mySocket, true);
}
catch (IOException e) {
System.out.print("Failed to set up server!");
}
Will stop the window from getting painted until a connection is made, at which time you dispose of the window any way.
You might like to take a read through
The Event Dispatching Thread
Concurrency in Swing
I'd suggest moving the the "connection" code into a SwingWorker and using it's done method to dispose of the window.

Do Robot methods need to be run on the event queue?

Robot is part of the AWT library, but it seems quite different from most all the rest of the library. I am creating a Swing GUI that mixes Swing with Java Native Access (JNA) and Robot to allow Java to drive some MS Windows/Citrix work programs. My gut feeling is that since Robot will queue events on the "platform's native input queue" that the last thing I want to do is to run it on the EDT, but on the other hand, most of the classes in the AWT and Swing libraries should be run on the Swing event thread. So to try clarify this in my mind for me let me ask as specific a question as possible:
Should Robot methods (in particular key presses and releases, mouse moves, mouse presses and releases) be run on or off of the Swing event dispatch thread (the EDT)?

The Robot methods you mentioned should not be run on the EDT. Taking a look at the source code revealed that each one of these "event" methods has one thing in common (the afterEvent call):
public synchronized void keyPress(int keycode) {
checkKeycodeArgument(keycode);
peer.keyPress(keycode);
afterEvent();
}
public synchronized void mousePress(int buttons) {
checkButtonsArgument(buttons);
peer.mousePress(buttons);
afterEvent();
}
// etc
private void afterEvent() {
autoWaitForIdle();
autoDelay();
}
private void autoWaitForIdle() {
if (isAutoWaitForIdle) {
waitForIdle();
}
}
public synchronized void waitForIdle() {
checkNotDispatchThread();
/* snip */
}
private void checkNotDispatchThread() {
if (EventQueue.isDispatchThread()) {
throw new IllegalThreadStateException("Cannot call method from the event dispatcher thread");
}
}
If you call any of these methods on the EDT while Robot.isAutoWaitForIdle is true, an exception will be thrown. This stands to reason that even if isAutoWaitForIdle is false, these methods shouldn't be called from the EDT.

API quite exactly talks, then I'm understand that that Robot should be ignore if is invoked from EDT or not
Using the class to generate input events differs from posting events to the AWT event queue or AWT components in that the events are generated in the platform's native input queue.
I'm rellative new in Java, my first touch was Java1.6.009, then I can't compare changes for AWT and (when born) Swing in Java1.3 and rest in Java1.4
my example
import javax.imageio.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;
import java.io.*;
public class CaptureScreen implements ActionListener {
private JFrame f = new JFrame("Screen Capture");
private JPanel pane = new JPanel();
private JButton capture = new JButton("Capture");
private JDialog d = new JDialog();
private JScrollPane scrollPane = new JScrollPane();
private JLabel l = new JLabel();
private Point location;
public CaptureScreen() {
capture.setActionCommand("CaptureScreen");
capture.setFocusPainted(false);
capture.addActionListener(this);
capture.setPreferredSize(new Dimension(300, 50));
pane.add(capture);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.add(pane);
f.setLocation(100, 100);
f.pack();
f.setVisible(true);
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
createPicContainer();
}
});
}
private void createPicContainer() {
l.setPreferredSize(new Dimension(700, 500));
scrollPane = new JScrollPane(l,
ScrollPaneConstants.VERTICAL_SCROLLBAR_AS_NEEDED,
ScrollPaneConstants.HORIZONTAL_SCROLLBAR_AS_NEEDED);
scrollPane.setBackground(Color.white);
scrollPane.getViewport().setBackground(Color.white);
d.setDefaultCloseOperation(JDialog.HIDE_ON_CLOSE);
d.add(scrollPane);
d.pack();
d.setVisible(false);
}
#Override
public void actionPerformed(ActionEvent e) {
if (e.getActionCommand().equals("CaptureScreen")) {
Dimension d1 = Toolkit.getDefaultToolkit().getScreenSize(); // gets the screen size
Robot r;
BufferedImage bI;
try {
r = new Robot(); // creates robot not sure exactly how it works
Thread.sleep(1000); // waits 1 second before capture
bI = r.createScreenCapture(new Rectangle(d1)); // tells robot to capture the screen
showPic(bI);
saveImage(bI);
} catch (AWTException e1) {
e1.printStackTrace();
} catch (InterruptedException e2) {
e2.printStackTrace();
}
}
}
private void saveImage(BufferedImage bI) {
try {
ImageIO.write(bI, "JPG", new File("screenShot.jpg"));
} catch (IOException e) {
e.printStackTrace();
}
}
private void showPic(BufferedImage bI) {
ImageIcon pic = new ImageIcon(bI);
l.setIcon(pic);
l.revalidate();
l.repaint();
d.setVisible(false);
location = f.getLocationOnScreen();
int x = location.x;
int y = location.y;
d.setLocation(x, y + f.getHeight());
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
d.setVisible(true);
}
});
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
CaptureScreen cs = new CaptureScreen();
}
});
}
}

Amplifying on #mKorbel's thoughtful answer, and confirming his empirical result, note how the various Robot methods delegate to an internal instance of the RobotPeer interface, the native implementation of which varies by platform. Moreover, the methods are synchronized. The synthetic events all arrive on the EventQueue, irrespective of the source.