We are looking at the variety of components that are available to combine with layout and event handling to produce an effective GUI.
| "A class that produces a dialog - a window that takes input from the
user. The default layout for a dialog is BorderLayout.
Dialogs are capable of generating the following window events: WindowOpened, WindowClosing, WindowClosed, WindowActivated, WindowDeactivated." |
As of 3/14/97, the Dialog class has no fields and has
the following public constructors:
|
The boolean parameter in two versions of the constructor determines
whether or not the Dialog object is modal. According to the
JDK 1.1 documentation:
| "A modal Dialog grabs all the input from the user." |
Note that the Dialog object can also be made modal after it is instantiated using the setModal() method.
As of 3/14/97, the Dialog class has nine methods, and inherits
many more methods from its superclasses. An interesting subset of the methods
in the Dialog class is shown below:
|
| "Shows the dialog. This will bring the dialog to the front if the dialog
is already visible. If the dialog is modal, this call will block until
the dialog is taken down by calling hide or dispose.
It is permissible to show modal dialogs from the event dispatching thread because the toolkit will ensure that another dispatching thread will run while the one which invoked show is blocked." |
The purpose of this program is to illustrate the minimum code necessary to get a Dialog object to appear on the screen. The following description is based on executing this program under JDK 1.1.3 and Win95.
When the program starts, a Frame object and a Dialog object should both appear on the screen. The Dialog object should be about half the size of the Frame object in both dimensions.
The Dialog object should contain a title and a close box. However, the close box is not operative.
The Dialog object can be moved and it can be resized. It does not have a minimize button or a maximize button, but the control box in the upper left-hand corner can be used to minimize and maximize the object. The Dialog object can be placed anywhere on the screen. Its position is not restricted to the interior of its parent, the Frame object.
On a Win95 system, the Frame object has a white background and the Dialog object has a grey background. (This may depend on some of the setup parameters in Win95.) When the title bar is selected on either object, the title bar has a blue background and white letters.
The Frame object appears to have a border while the Dialog object does not appear to have a border. It differs in appearance from the Frame object.
The program was tested using JDK 1.1.3 running under Win95.
Note that the Dialog, when created using JDK 1.1.3 under Win 95, has both a close box in the upper right-hand corner and a control box in the upper left-hand corner. Although it doesn't have minimize and maximize buttons, those capabilities exist, and are active in the control box. It is the opinion of this author that it would be better if it were possible to create a Dialog without these controls showing.
Dialog myDialog = new Dialog(this,"Dialog"); myDialog.setSize(125,75); myDialog.show();//make the Dialog object appear |
/*File Dialog01.java Copyright 1997, R.G.Baldwin
This program is designed to be compiled and run under
JDK 1.1
The purpose of this program is to illustrate the minimum
code requirement to get a Dialog object to appear on the
screen
The program was tested using JDK 1.1.3 running under Win95.
**********************************************************/
import java.awt.*;
import java.awt.event.*;
//=======================================================//
public class Dialog01 extends Frame{
public static void main(String[] args){
new Dialog01();//instantiate an object of this type
}//end main
public Dialog01(){//constructor
setTitle("Copyright 1997, R.G.Baldwin");
setSize(250,150);
setVisible(true);
Dialog myDialog = new Dialog(this,"Dialog");
myDialog.setSize(125,75);
myDialog.show();//make the Dialog object appear
}//end constructor
}//end class Dialog01
//=======================================================// |
A Frame object which will serve as the parent of two Dialog objects is instantiated. Since it will serve as a parent, it must be instantiated first.
A nonModal Dialog object is created containing a Button object. The Button object is used to close the Dialog object.
An ActionListener object is instantiated and registered on the Button object which belongs to the Dialog object.
This ActionListener object is instantiated from a shared ActionListener class. Code in the overridden actionPerformed() method of the ActionListener object closes the Dialog object by invoking setVisible(false). According to the previous description of the show() method, it would also have been possible to use hide() or dispose() to close the Dialog object.
A Modal Dialog object is created in the same manner. It also containing a Button object. As with the nonModal Dialog object, the Button object shares the same ActionListener class to invoke the setVisible(false) method to close the Modal Dialog object.
Two Button objects are created and placed on the Frame object. One is designed to show the nonModal Dialog object and the other is designed to show the Modal Dialog object.
These two Button objects share a common ActionListener class that is designed to show a Dialog object at a predefined size and a parameterized location. The location of the Dialog object is controlled by an integer offset parameter that is passed when the ActionListener object is instantiated.
To avoid overlap, the ActionListener objects for the two Button objects that show the Dialog objects in this program are instantiated with different offset values. Then when the Dialog objects are shown, they appear at different locations on the screen.
If you compile and run this program, it should begin with two Button objects visible. One of the Button objects can be used to show the nonModal Dialog object. The other can be used to show the Modal Dialog object. When the Modal Dialog object is not visible, you can show and close the nonModal Dialog object at will. You can also click the close box on the Frame object to terminate the program.
However, when the Modal Dialog is visible, you should not be able to perform any other operation within this program, but you should be able to start other programs. This mode of operation is sometimes referred to as "application modal".
When the Modal Dialog object is showing on a Win95 system and you attempt to perform some other operation within the program, you may receive an audible signal, possibly depending on how you have the sounds set up on your system.
A windowClosing() event listener object is instantiated and registered on the frame to terminate the program when the frame is closed. However, the frame cannot be closed while the Modal Dialog object is visible.
The program was tested using JDK 1.1.3 running under Win95.
Frame myFrame = new Frame("Copyright 1997, R.G.Baldwin"); |
|
Dialog modalDialog =
new Dialog(myFrame,"Modal Dialog",true);
Button modalCloseButn = new Button("Close");
modalDialog.add(modalCloseButn);
modalCloseButn.addActionListener(
new closeDialogListener(modalDialog)); |
The code to instantiate the Button objects is followed by code to finish constructing the Frame object. Again, this is old stuff for us by now.
The next interesting code fragment is the ActionListener class used to instantiate objects for showing a Dialog object.
Two aspects of this code are interesting. First, a parameterized constructor is used to save an offset value passed in as a parameter when the ActionListener object is instantiated. This offset value is combined with literal values in the code to control both the size and the location location of the Dialog object when it appears on the screen.
The second interesting aspect is that the show() method of the Dialog class is used to actually cause the Dialog object to appear on the screen.
Note also that the order of execution of the statements within
the overridden actionPerformed() method is critical. If the show()
method is executed before the setBounds() method on the Modal
Dialog object, the setBounds() method used to control
the location and size of the Dialog object has no effect. The size
and location of the Modal Dialog object must be established
before it becomes visible.
class showDialogListener implements ActionListener{
Dialog aDialog;
int Offset;
//constructor
showDialogListener(Dialog inDialog,int inOffset){
aDialog = inDialog;
Offset = inOffset;
}//end constructor
public void actionPerformed(ActionEvent e){
//Following order is critical for a modal dialog.
aDialog.setBounds(Offset,Offset,150,100);
aDialog.show();
}//end actionPerformed()
}//end class myModalActionListener |
public void actionPerformed(ActionEvent e){
aDialog.setVisible(false);
}//end actionPerformed() |
/*File Dialog02.java Copyright 1997, R.G.Baldwin
This program is designed to be compiled and run under
JDK 1.1
A Frame object which will serve as the parent of two
Dialog objects is instantiated. Since it will serve as a
parent, it must be instantiated first.
A nonModal Dialog object is created containing a Button
object. The Button object is used to close the Dialog
object. An ActionListener object is instantiated and
registered on the Button object. This object is
instantiated from a shared ActionListener class. Code in
the overridden actionPerformed() method of the
ActionListener object closes the Dialog object by invoking
setVisible(false).
A Modal Dialog object is created also containing a Button
object. As with the nonModal Dialog object, the Button
object shares the same ActionListener class to invoke the
setVisible(false) method to close the Modal Dialog object.
Two Button objects are created and placed on the Frame
object. One is designed to show the nonModal Dialog
object and the other is designed to show the Modal Dialog
object. These two Button objects share a common
ActionListener class that is designed to show a Dialog
object at a predefined size. The position of the dialog
object is controlled by an integer offset parameter that
is passed when the ActionListener object is instantiated.
To avoid overlap, the ActionListener objects for the two
Button objects that show the Dialog objects are
instantiated with different offset values. Then when the
Dialog objects are shown, they appear at different
locations on the screen.
If you compile and run this program, it should begin with
two Button objects visible. One of the Button objects can
be used to show the nonModal Dialog object. The other can
be used to show the Modal Dialog object. When the Modal
Dialog is showing, you should not be able to perform any
other operation within this program, but you should be
able to start other programs. This mode of operation is
sometimes referred to as "application modal". When the
Modal Dialog is showing on a Win95 system and you attempt
to perform some other operation within the program, you
may receive an audible signal, possibly depending on how
you have the sounds set up on your system.
A windowClosing() event listener object is instantiated
and registered on the frame to terminate the program when
the frame is closed. However, the Frame cannot be closed
while the Modal Dialog is showing.
The program was tested using JDK 1.1.3 running under Win95.
**********************************************************/
import java.awt.*;
import java.awt.event.*;
//=======================================================//
public class Dialog02 {
public static void main(String[] args){
GUI gui = new GUI();//instantiate a GUI
}//end main
}//end class Dialog02
//=======================================================//
class GUI {
public GUI(){//constructor
//Instantiate a Frame object to serve as the parent of
// two Dialog objects. Since it will be the parent, it
// must be instantiated first.
Frame myFrame = new Frame(
"Copyright 1997, R.G.Baldwin");
//Create a nonModal Dialog object containing a close
// button with an action listener object registered
// on the close button.
Dialog nonModalDialog =
new Dialog(myFrame,"NonModal Dialog");
Button nonModalCloseButn = new Button("Close");
nonModalDialog.add(nonModalCloseButn);
nonModalCloseButn.addActionListener(
new closeDialogListener(nonModalDialog));
//Create a Modal Dialog object containing a close
// button with an action listener object registered on
// the close button.
Dialog modalDialog =
new Dialog(myFrame,"Modal Dialog",true);
Button modalCloseButn = new Button("Close");
modalDialog.add(modalCloseButn);
modalCloseButn.addActionListener(
new closeDialogListener(modalDialog));
//Create two Button objects to appear on the Frame
// object. One Button object will show the nonModal
// Dialog object. The other button will show the
// Modal Dialog object. Instantiate and register
// action listener objects on both buttons which will
// show the Dialog object passed in as a parameter at
// the X/Y offset also passed in as a parameter. The
// action listener objects also control the size of
// the Dialog objects.
Button showNonModalButn =
new Button("Show NonModal Dialog");
showNonModalButn.addActionListener(
new showDialogListener(nonModalDialog,100));
Button showModalButn = new Button("Show Modal Dialog");
showModalButn.addActionListener(
new showDialogListener(modalDialog,200));
//Now finish constructing the Frame object.
myFrame.setLayout(new FlowLayout());
myFrame.add(showModalButn);
myFrame.add(showNonModalButn);
myFrame.setSize(250,150);
myFrame.setVisible(true);
//Instantiate and register a window listener to
// terminate the program when the Frame is closed.
myFrame.addWindowListener(new Terminate());
}//end constructor
}//end class GUI definition
//=======================================================//
//Class to provide an action listener that will show a
// Dialog specified as a parameter at the X/Y offset also
// passed in as a parameter. The action listener object
// also controls the size of the Dialog objects.
class showDialogListener implements ActionListener{
Dialog aDialog;
int Offset;
//constructor
showDialogListener(Dialog inDialog,int inOffset){
aDialog = inDialog;
Offset = inOffset;
}//end constructor
public void actionPerformed(ActionEvent e){
//Following order is critical for a modal dialog.
aDialog.setBounds(Offset,Offset,150,100);
aDialog.show();
}//end actionPerformed()
}//end class myModalActionListener
//=======================================================//
//Class to provide an action listener that will close a
// Dialog specified as a parameter.
class closeDialogListener implements ActionListener{
Dialog aDialog;
closeDialogListener(Dialog inDialog){//constructor
aDialog = inDialog;
}//end constructor
public void actionPerformed(ActionEvent e){
aDialog.setVisible(false);
}//end actionPerformed()
}//end class myModalAdtionListener
//=======================================================//
class Terminate extends WindowAdapter{
public void windowClosing(WindowEvent e){
System.exit(0);//terminate the program
}//end windowClosing
}//end class Terminate
//=======================================================// |
Therefore, review questions and programs will rarely be provided for the remaining lessons in this set of Java programming tutorials.
-end-
These tutorials were developed by Richard Baldwin and are the copyrighted property of Richard Baldwin. You have permission to print one copy for your own use, but may not, without written permission from Richard Baldwin, redistribute the tutorial documents. The base material in these lessons is believed by the author to be in the public domain. If you use these lessons for any purpose, you are using them at your own risk, and this author assumes no responsibility or liability for any damages that you may incur.
Java, Sun, HotJava and various other related symbols and names are registered trademarks of Sun Microsystems, Inc. Macintosh is a registered trademark of Apple Computer, Inc. OS/2 is a registered trademark of International Business Machines Corporation. Microsoft, MS-DOS, Visual Basic, Windows, Windows NT, Internet Explorer and Visual J++ are registered trademarks of Microsoft Corporation. Netscape and JavaScript are trademarks of Netscape Communications Corporation. All other trademarks and service marks that may have been inadvertently used in these lessons without proper credit being given are the property of their respective owners. If you feel that your trademark or copyright has been compromised, please notify this author immediately, and an appropriate correction to the document will be issued.
© 1996, 1997, 1998, 1999 Richard G. Baldwin