ch4.htm

JAVA Developing Professional JavaApplets

is called before a window is displayed. Windows are not made visible
until the <TT>show()</TT> method is
called. They are removed from the screen, and their resources
freed, when the <TT>dispose()</TT>
method is invoked.
<P>
The Frame class extends Window by adding a title bar, a border
for resizing, support for menus, and the ability to modify the
system cursor to various states such as waiting or moving. For
most GUI platforms, the Frame's title bar will be tied to system
control boxes, such as minimize, maximize, or destroy. Consequently,
the Frame class has all the elements necessary to make an applet
look like a &quot;real&quot; application, complete with menus
and system controls.
<P>
Figure 4.1 and Listing 4.1 present a simple Frame applet that
changes the cursor to a state based on the button selected. The
applet class, FrameCursorApplet, does little more than launch
the main frame, FrameCursor. The constructor for this frame begins
by calling the frame super constructor. The sole parameter in
this case is the caption displayed on the title bar. The layout
for the Frame is then set. The default is BorderLayout, but in
this case, you want a three by two grid matrix, hence the use
of GridLayout. The buttons are added to the frame next, with names
representing the cursor state to be selected. After all the components
have been added, the <TT>pack()</TT>
method is invoked so that the button placement can be optimized.
Since this optimized placement will result in a small frame (six
buttons sized tightly around the label text doesn't take much
space), the <TT>resize()</TT> method
is called to make the frame a larger size. Finally, the frame
is displayed with the <TT>show()</TT>
method.
<P>
<A HREF="f4-1.gif" >Figure 4.1 : <I>Frame applets for changing the state of the cursor.</I></A>
<P>
When a button is selected, the custom method <TT>SetCursor()</TT>
is invoked. This method takes the button label and figures out
which cursor should be displayed. The Frame <TT>setCursor()</TT>
method is used to set the cursor state; its parameter is a static
integer defined as part of the Frame class.<BR>
<P><CENTER><TABLE BORDERCOLOR=#000000 BORDER=1 WIDTH=80%>
<TR VALIGN=TOP><TD><B>Note</B></TD></TR>
<TR VALIGN=TOP><TD>
<BLOCKQUOTE>
You might see the message <TT><FONT SIZE=1 FACE="Courier">Untrusted Java Applet Window</TT></FONT> in your Netscape browser when applet frames are displayed. However, this is not cause for alarm-it is just a security message.
</BLOCKQUOTE>

</TD></TR>
</TABLE></CENTER>
<P>
<HR>
<BLOCKQUOTE>
<B>Listing 4.1. Code for Frame applet that changes the cursor
state.<BR>
</B>
</BLOCKQUOTE>
<BLOCKQUOTE>
<TT>import java.awt.*;<BR>
import java.lang.*;<BR>
import java.applet.*;<BR>
<BR>
// This applet simply starts up the frame used to<BR>
// show different frame cursors...<BR>
public class FrameCursorApplet extends Applet&nbsp;&nbsp;{<BR>
&nbsp;&nbsp;&nbsp;&nbsp;public void init() {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Create the frame with a
title...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;new FrameCursor(&quot;Frame
Cursors&quot;);<BR>
&nbsp;&nbsp;&nbsp;}<BR>
}<BR>
<BR>
// The frame for letting the user pick different<BR>
// cursors to display...<BR>
class FrameCursor extends Frame {<BR>
&nbsp;&nbsp;&nbsp;// Create the frame with a title...<BR>
&nbsp;&nbsp;&nbsp;public FrameCursor(String title) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Call the superclass constructor...
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;super(title);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Create a grid layout to
place the buttons...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;setLayout(new GridLayout(3,2));
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Add the buttons for choosing
the cursor...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;add(new Button(&quot;Default&quot;));
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;add(new Button(&quot;Wait&quot;));
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;add(new Button(&quot;Hand&quot;));
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;add(new Button(&quot;Move&quot;));
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;add(new Button(&quot;Text&quot;));
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;add(new Button(&quot;SE Resize&quot;));
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Pack and display...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;pack();<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;resize(300,200); // Make it
a reasonable size...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;show();<BR>
&nbsp;&nbsp;&nbsp;}<BR>
<BR>
&nbsp;&nbsp;&nbsp;// Handle events...<BR>
&nbsp;&nbsp;&nbsp;public boolean handleEvent(Event e) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;switch(e.id) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;case e.WINDOW_DESTROY:
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;dispose();&nbsp;&nbsp;//
Erase frame<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return
true;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;case
Event.ACTION_EVENT:<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if
(e.target instanceof Button)<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;SetCursor((Button)e.target);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return
true;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;default:
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return
false;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;}<BR>
<BR>
&nbsp;&nbsp;&nbsp;// Set the cursor based on the button chosen...
<BR>
&nbsp;&nbsp;&nbsp;void SetCursor(Button btn) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Get the label of the button...
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;String selection = btn.getLabel();
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;//Set the cursor based on
that label...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if (selection.equals(&quot;Wait&quot;))
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;setCursor(Frame.WAIT_CURSOR);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;else if (selection.equals(&quot;Hand&quot;))
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;setCursor(Frame.HAND_CURSOR);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;else if (selection.equals(&quot;Move&quot;))
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;setCursor(Frame.MOVE_CURSOR);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;else if (selection.equals(&quot;Text&quot;))
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;setCursor(Frame.TEXT_CURSOR);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;else if (selection.equals(&quot;SE
Resize&quot;))<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;setCursor(Frame.SE_RESIZE_CURSOR);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;else // Just use the default...
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;setCursor(Frame.DEFAULT_CURSOR);
<BR>
&nbsp;&nbsp;&nbsp;}<BR>
}</TT>
</BLOCKQUOTE>
<HR>
<P>
The current state of the cursor can be retrieved with the <TT>getCursorType()</TT>
method, and the <TT>getTitle()</TT>
and <TT>setTitle()</TT> Frame methods
can be used for getting and setting the title bar caption, respectively.
Similarly, the <TT>getIconImage()</TT>
and <TT>setIconImage()</TT> methods
can be used to set the image display of an iconized frame.
<H3><A NAME="Menus">Menus</A></H3>
<P>
Frames and menus are closely related since the Frame class is
the only AWT class with built-in support for menus. Frames implement
the MenuContainer interface, which is used to contain menu components.
These components are defined by the MenuComponent class, the superclass
of all menu components. It defines a set of methods pertinent
to individual menu items. For example, the <TT>getFont()</TT>
and <TT>setFont()</TT> MenuComponent
methods are used to control the font selection of the menu object.
<P>
Menus can be illustrated by modifying the previous example to
use menus, instead of buttons, to change the state of a cursor.
Listing 4.2 shows the code that performs this. The constructor
of the Frame class, called FrameMenuCursor, shows how to add menus
to a frame. The first step is creating a MenuBar object. The menu
bar is tied to the frame with the <TT>setMenuBar()</TT>
method of the Frame class. This makes the MenuBar object the default
menu for the frame.
<P>
The next step is to add the individual menus to the menubar. The
Menu class is used as a container of individual menu items or
other menus. In this applet, the two menus are File and Cursor.
The Menu constructor takes these strings as its sole parameter,
thus defining the text to be associated with the menu. The menus
are then added to the menu bar through the MenuBar <TT>add()</TT>
method. The <TT>remove()</TT> method
can be used to delete a Menu from a MenuBar.
<P>
The final step in menu creation is to add the individual menu
items, defined by the MenuItem class. This class is a subclass
of MenuComponent and provides additional operations to be performed
on a menu item. MenuItem methods can be used to set the menu label
and to disable or enable an item. The constructor for the MenuItem
has as its sole parameter the item label that will be initially
displayed. The <TT>add()</TT> method
is used to add an instance of MenuItem to a Menu.
<HR>
<BLOCKQUOTE>
<B>Listing 4.2. Code for applet that uses menus to change cursor
state.<BR>
</B>
</BLOCKQUOTE>
<BLOCKQUOTE>
<TT>import java.awt.*;<BR>
import java.lang.*;<BR>
import java.applet.*;<BR>
<BR>
// This applet simply starts up the frame<BR>
// which provides a menu for setting cursors...<BR>
public class FrameMenuCursorApplet extends Applet {<BR>
&nbsp;&nbsp;&nbsp;public void init() {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Create the frame with a
title...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;new FrameMenuCursor(&quot;Menu
Based Cursors&quot;);<BR>
&nbsp;&nbsp;&nbsp;}<BR>
}<BR>
<BR>
// The frame for letting the user pick different<BR>
// cursors to display...<BR>
class FrameMenuCursor extends Frame {<BR>
&nbsp;&nbsp;&nbsp;// Create the frame with a title...<BR>
&nbsp;&nbsp;&nbsp;public FrameMenuCursor(String title) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Call the superclass constructor...
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;super(title);<BR>
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Add the menus...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// First create the menu bar
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;MenuBar mbar = new MenuBar();
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;setMenuBar(mbar); // Attach
to the frame...<BR>
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Add the File submenu...
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Menu m = new Menu(&quot;File&quot;);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;mbar.add(m);&nbsp;&nbsp;//
Add to menu bar<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Add Quit to the submenu...
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;m.add(new MenuItem(&quot;Quit&quot;));
<BR>
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Add the Cursor submenu...
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;m = new Menu(&quot;Cursor&quot;);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;mbar.add(m);&nbsp;&nbsp;//
Add to menu bar<BR>
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Add the cursor selections
to the submenu...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;m.add(new MenuItem(&quot;Default&quot;));
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;m.add(new MenuItem(&quot;Wait&quot;));
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;m.add(new MenuItem(&quot;Hand&quot;));
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;m.add(new MenuItem(&quot;Move&quot;));
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;m.add(new MenuItem(&quot;Text&quot;));
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;m.add(new MenuItem(&quot;SE
Resize&quot;));<BR>
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Pack and display...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;pack();<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;resize(300,200); // Make it
a reasonable size...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;show();<BR>
&nbsp;&nbsp;&nbsp;}<BR>
<BR>
&nbsp;&nbsp;&nbsp;// Handle events...<BR>
&nbsp;&nbsp;&nbsp;public boolean handleEvent(Event e) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;switch(e.id) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;case e.WINDOW_DESTROY: