One way is to do get the taskbar's handle and send it a message to hide all windows, perhaps something like this which has worked for me on Windows 7:
import com.sun.jna.Native;
import com.sun.jna.platform.win32.WinDef.HWND;
import com.sun.jna.win32.W32APIOptions;
public class ToggleDesktop3 {
public interface User32 extends W32APIOptions {
public static final String SHELL_TRAY_WND = "Shell_TrayWnd";
public static final int WM_COMMAND = 0x111;
public static final int MIN_ALL = 0x1a3;
public static final int MIN_ALL_UNDO = 0x1a0;
User32 instance = (User32) Native.loadLibrary("user32", User32.class,
DEFAULT_OPTIONS);
HWND FindWindow(String winClass, String title);
long SendMessageA(HWND hWnd, int msg, int num1, int num2);
}
public static void main(String[] args) {
// get the taskbar's window handle
HWND shellTrayHwnd = User32.instance.FindWindow(User32.SHELL_TRAY_WND,
null);
// use it to minimize all windows
User32.instance.SendMessageA(shellTrayHwnd, User32.WM_COMMAND,
User32.MIN_ALL, 0);
// sleep for 3 seconds
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
}
// then restore previously minimized windows
User32.instance.SendMessageA(shellTrayHwnd, User32.WM_COMMAND,
User32.MIN_ALL_UNDO, 0);
}
}
There looks to be another way to do this via Shell32 library calls (something involving the ToggleDesktop function -- for a C# version, check out this SO link), but I've not gotten it to work yet.