Next, the window is sized using this statement:
jfrm.setSize(275, 100);
The setSize( ) method (which is inherited by JFrame from the AWT class Component) sets
the dimensions of the window, which are specified in pixels. Its general form is shown here:
void setSize(int width, int height)
In this example, the width of the window is set to 275 and the height is set to 100.
By default, when a top-level window is closed (such as when the user clicks the close
box), the window is removed from the screen, but the application is not terminated. While
this default behavior is useful in some situations, it is not what is needed for most applications.
Instead, you will usually want the entire application to terminate when its top-level
window is closed. There are a couple of ways to achieve this. The easiest way is to call
setDefaultCloseOperation( ), as the program does:
jfrm.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
After this call executes, closing the window causes the entire application to terminate. The
general form of setDefaultCloseOperation( ) is shown here:
void setDefaultCloseOperation(int what)
The value passed in what determines what happens when the window is closed. There are
several other options in addition to JFrame.EXIT_ON_CLOSE. They are shown here:
JFrame.DISPOSE_ON_CLOSE
JFrame.HIDE_ON_CLOSE
JFrame.DO_NOTHING_ON_CLOSE
Their names reflect their actions. These constants are declared in WindowConstants, which
is an interface declared in javax.swing that is implemented by JFrame.
The next line of code creates a Swing JLabel component:
JLabel jlab = new JLabel(" Swing means powerful GUIs.");
JLabel is the simplest and easiest-to-use component because it does not accept user input. It
simply displays information, which can consist of text, an icon, or a combination of the two.
The label created by the program contains only text, which is passed to its constructor.
The next line of code adds the label to the content pane of the frame:
jfrm.add(jlab);
As explained earlier, all top-level containers have a content pane in which components are
stored. Thus, to add a component to a frame, you must add it to the frame's content pane.
This is accomplished by calling add( ) on the JFrame reference (jfrm in this case). The
general form of add( ) is shown here:
Component add(Component comp)
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