ch6.htm

JAVA Developing Professional JavaApplets

<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;String fieldParam;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;String selectParam;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Add first row of field
and display image...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if (((fieldParam = getParameter(&quot;field1&quot;))
!= null) &amp;&amp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;((selectParam
= getParameter(&quot;image1&quot;)) != null) ) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; button[0] = createCatalogButton(fieldParam,data[0]);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; drawing[0] = new SelectionCanvas(this,
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;selectParam,getDocumentBase());
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; button[0].resize(150,100);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; drawing[0].resize(250,100);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;} // end if<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;else {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; getAppletContext().showStatus(&quot;Invalid
parameter&quot;);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; button[0] = null;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Add second row of field
and display image...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if (((fieldParam = getParameter(&quot;field2&quot;))
!= null) &amp;&amp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;((selectParam
= getParameter(&quot;image2&quot;)) != null) ) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; button[1] = createCatalogButton(fieldParam,data[1]);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; drawing[1] = new SelectionCanvas(this,
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;selectParam,getDocumentBase());
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; drawing[1].resize(250,100);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; button[1].resize(150,100);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;} // end if<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;else {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; getAppletContext().showStatus(&quot;Invalid
parameter&quot;);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; button[1] = null;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Add third row of field
and display image...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if (((fieldParam = getParameter(&quot;field3&quot;))
!= null) &amp;&amp;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;((selectParam
= getParameter(&quot;image3&quot;)) != null) ) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; button[2] = createCatalogButton(fieldParam,data[2]);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; drawing[2] = new SelectionCanvas(this,
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;selectParam,getDocumentBase());
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; button[2].resize(150,100);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; drawing[2].resize(250,100);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;} // end if<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;else {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; getAppletContext().showStatus(&quot;Invalid
parameter&quot;);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; button[2] = null;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;}<BR>
<BR>
&nbsp;&nbsp;&nbsp;// Load additional data from URL...<BR>
&nbsp;&nbsp;&nbsp;void loadURLData() {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;// Get path to data from parameter...
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;String dataPath = getParameter(&quot;data&quot;);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;if (dataPath == null) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;System.out.println(&quot;No
data variable found&quot;);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;} // end if<BR>
&nbsp;&nbsp;&nbsp;&nbsp;// Create URL for data...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;URL u;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;try {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;u = new URL(getDocumentBase(),dataPath);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;catch (MalformedURLException e) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;System.out.println(&quot;Bad
Data URL&quot;);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;// Now load the data by opening up a stream
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;// to the URL...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;try {<BR>
&nbsp;&nbsp;&nbsp;&nbsp; DataInputStream dis = new DataInputStream(
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;new BufferedInputStream(<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;u.openStream()
) );<BR>
&nbsp;&nbsp;&nbsp;&nbsp; // Read only the first three lines...
<BR>
&nbsp;&nbsp;&nbsp;&nbsp; int i;<BR>
&nbsp;&nbsp;&nbsp;&nbsp; for (i = 0; i &lt; 3; ++i) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;data[i]
= dis.readLine();<BR>
&nbsp;&nbsp;&nbsp;&nbsp; } // end for<BR>
&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;catch (IOException e) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;System.out.println(&quot;URL
read error&quot;);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;}<BR>
<BR>
&nbsp;&nbsp;&nbsp;// Update message sent when repainting is needed...
<BR>
&nbsp;&nbsp;&nbsp;// Prevent paint from getting cleared out...
<BR>
&nbsp;&nbsp;&nbsp;public void update(Graphics g) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;paint(g);<BR>
&nbsp;&nbsp;&nbsp;}<BR>
<BR>
&nbsp;&nbsp;&nbsp;// Repaint all the canvas components...<BR>
&nbsp;&nbsp;&nbsp;public synchronized void paint(Graphics g) {
<BR>
&nbsp;&nbsp;&nbsp;&nbsp; int i,x,y;<BR>
&nbsp;&nbsp;&nbsp;&nbsp; Dimension dm;<BR>
&nbsp;&nbsp;&nbsp;&nbsp; int defHeight = 150;<BR>
<BR>
&nbsp;&nbsp;&nbsp;&nbsp; // Go through the buttons...<BR>
&nbsp;&nbsp;&nbsp;&nbsp; for (x = y = i = 0; i &lt; 3; ++i) {
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if (button[i] != null) {
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;button[i].paint(g,x,y);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;dm = button[i].size();
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;x += dm.width;
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;drawing[i].paint(g,x,y);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;x = 0;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;y += dm.height;
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; }<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; else<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;y += defHeight;
<BR>
&nbsp;&nbsp;&nbsp;&nbsp; } // end for<BR>
&nbsp;&nbsp;&nbsp;}<BR>
<BR>
 public boolean mouseDown(Event ev, int x, int y) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// See if you clicked on any
of the buttons...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;for (int i = 0; i &lt; 3;
++i) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if ((button[i]
!= null) &amp;&amp; (button[i].inside(x,y)) ) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;System.out.println(&quot;Hit
Button &quot; + i);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;//
Link to the button's selected field...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;button[i].select();
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;break;
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;&nbsp;//
end if<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return true;<BR>
 };<BR>
<BR>
&nbsp;&nbsp;&nbsp;// Parse a parameter and create catalog field...
<BR>
&nbsp;&nbsp;&nbsp;CatalogButton createCatalogButton(String param,String
data) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp; // Set up defaults...<BR>
&nbsp;&nbsp;&nbsp;&nbsp; String fieldName = &quot;&quot;;<BR>
&nbsp;&nbsp;&nbsp;&nbsp; String imageName = &quot;&quot;;<BR>
&nbsp;&nbsp;&nbsp;&nbsp; String style = &quot;MEDIUM&quot;;<BR>
&nbsp;&nbsp;&nbsp;&nbsp; String link = getDocumentBase().toString();
<BR>
&nbsp;&nbsp;&nbsp;&nbsp; // Parse out the string...<BR>
&nbsp;&nbsp;&nbsp;&nbsp; StringTokenizer s = new StringTokenizer(param,&quot;,&quot;);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp; if (s.hasMoreTokens()) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;fieldName = s.nextToken();
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if (s.hasMoreTokens()) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; imageName = s.nextToken();
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if (s.hasMoreTokens()) {
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;style =
s.nextToken();<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if (s.hasMoreTokens())
{<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;link
= s.nextToken();<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; } // end style if<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;} // end image if<BR>
&nbsp;&nbsp;&nbsp;&nbsp; } // end field if<BR>
&nbsp;&nbsp;&nbsp;&nbsp; // Figure out the style. Convert it all
to uppercase...<BR>
&nbsp;&nbsp;&nbsp;&nbsp; style = style.toUpperCase();<BR>
&nbsp;&nbsp;&nbsp;&nbsp; int styleType;<BR>
&nbsp;&nbsp;&nbsp;&nbsp; if (style.equals(&quot;MEDIUM&quot;))
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;styleType
= MEDIUM_STYLE;<BR>
&nbsp;&nbsp;&nbsp;&nbsp; else if (style.equals(&quot;SMALL&quot;))
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;styleType
= SMALL_STYLE;<BR>
&nbsp;&nbsp;&nbsp;&nbsp; else if (style.equals(&quot;LARGE&quot;))
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;styleType
= LARGE_STYLE;<BR>
&nbsp;&nbsp;&nbsp;&nbsp; else<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;styleType
= DEFAULT_STYLE;<BR>
<BR>
&nbsp;&nbsp;&nbsp;&nbsp; // Create button according to these parameters...
<BR>
&nbsp;&nbsp;&nbsp;&nbsp; return new CatalogButton(this,<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;imageName,fieldName,
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;styleFont[styleType],getDocumentBase(),
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;link,data,dataFont);
<BR>
&nbsp;&nbsp;&nbsp;}<BR>
}</TT>
</BLOCKQUOTE>
<HR>
<H3><A NAME="TheCatalogButtonClass">The CatalogButton Class</A>
</H3>
<P>
The CatalogButton class is used to represent the choices you can
make for each applet screen. It appears on the left-hand side
of the applet and goes to another URL when the button is selected.
This URL will represent another page in the catalog.
<P>
The CatalogButton constructor takes as input the main and sub
text fields, the corresponding fonts, the background image, and
a URL and relative path used to construct the URL the button will
link to. One of the key things about the class is that its Image
object is loaded through the MediaLoader class (described shortly)
and not through the applet's <TT>getImage()</TT>
method. This approach takes advantage of the caching techniques
that will be developed in the MediaLoader throughout this chapter.
<P>
The <TT>paint()</TT> method is invoked
by the Catalog class and passed the x-y coordinate where the image
should be painted on the applet. It draws the image by using the
<TT>drawImage()</TT> method. It then
draws a title field in the center of the button. The FontMetrics
are used to center the text. Finally, if an additional data field
exists, it is drawn underneath the title in a smaller font.
<P>
If the button is selected, the CatalogButton object changes its
text to white by setting an internal state variable and forcing
a repaint. It then creates a URL object out of the base URL and
its relative path. This URL represents the new catalog page in
which to link. If the URL is successfully created, it links to
the new page with the <TT>showDocument()</TT>
method. If there is an error, then a message is displayed on the
browser's status bar.
<HR>
<BLOCKQUOTE>
<B>Listing 6.8. The CatalogButton class.<BR>
</B>
</BLOCKQUOTE>
<BLOCKQUOTE>
<TT>import java.awt.*;<BR>
import java.lang.*;<BR>
import java.net.*;<BR>
import java.applet.*;<BR>
<BR>
// This class represents a button on the current page.<BR>
// It represents the lefthand element of a kiosk selection<BR>
// that has a background<BR>
// image and text describing what the button represents.<BR>
// The field has a link to the Web page it should go to<BR>
// if it is selected...<BR>
// Parent of button is responsible for sizing and setting<BR>
// correct position...<BR>
public class CatalogButton extends Canvas {<BR>
&nbsp;&nbsp;&nbsp;String text; // What to display on left side...
<BR>
&nbsp;&nbsp;&nbsp;String data; // Additional data<BR>
&nbsp;&nbsp;&nbsp;URL URLBase; // The base URL to link from...
<BR>
&nbsp;&nbsp;&nbsp;String link; // Where to link to relative to
base...<BR>
&nbsp;&nbsp;&nbsp;Image img; // Background image...<BR>
&nbsp;&nbsp;&nbsp;Font f; // Font to pain