When producing a GUI, we will need to create windows on the screen. The Swing API has a number of classes that enable a program to create a new window on the screen or to make use of an existing window.

The classes are:

• JWindow - allows a window without a border or a menu bar to be displayed;
• JFrame - allows a window with a border and possibly a menu bar to be displayed;
• JDialog - allows a dialog box to be displayed;
• JInternalFrame - allows a frame to be created inside an existing frame;
• JApplet - allows the frame of a WWW page to be accessed by a Java applet.

Here is a simple program that displays a new window on the screen:

0013: // Stage B: creating a window.                           // GetDateProg.java
0014: // Barry Cornelius, 22nd November 1999
0015: import javax.swing. JFrame;
0016: public class GetDateProg
0017: {
0018:    public static void main(final String[] pArgs)
0019:    {
0020:       final JFrame tJFrame = new JFrame("GetDateProg: Stage B");
0021:       tJFrame.setLocation(50, 100);
0022:       tJFrame.setSize(300, 200);
0023:       tJFrame.setVisible(true);
0024:    }
0025: }

The program creates an object of the class JFrame. One of JFrame's constructors allows you to choose the string that is put into the title bar of the window:

JFrame tJFrame = new JFrame("GetDateProg: Stage B");

The use of this class instance creation expression just creates the JFrame object: it does not display the window on the screen. This is done by a call of the method setVisible:

tJFrame.setVisible(true);

Unless you specify otherwise, when the window is displayed, it will be positioned in the top left-hand corner of the screen. The call:

tJFrame.setLocation(50, 100);

says that you want the top left-hand corner of the window to be positioned 50 pixels from the left-hand side of the screen and 100 pixels down from the top of the screen. And the call:

tJFrame.setSize(300, 200);

says that you want the window to be 300 pixels wide and 200 pixels high.

When this program is executed, it just displays a blank window on the screen. The result of executing this program is shown in the Figure.

The program has no code to understand the removal of the window: so if you want to stop the execution of this program, you will need to press Ctrl/C in the window in which you typed the command:

java GetDateProg