I am doing a GUI project using SWING, there is a requirement that I am not sure if can be done by swing.
1. When the application start, the main window appears but kind of grey out, on top of the main window there is another small log in window for user to input user name and password, after the user input info and submit it and validation (using web service) is passed, then the login window disappear and the main window become the focus. On main window, there is log out button, when the button is clicked, the main window is grey out again and log in window appear on top of main window.
What you need is a modal window (modal indicates that the user cannot interact with the main window until the operations of the child window are done)
Check out the JOptionPane class. It has several convenient methods called showXXXDialog which you can use to display a modal dialog.
As for the graying out part, I personally feel you are thinking on the lines of a web based browser application. In my opinion the graying is not required in a stand alone application. However, if you still wish to have it, check out JFrame#setGlassPane.