ch5.htm

JAVA Developing Professional JavaApplets

&nbsp;&nbsp;&nbsp;int graphMode;<BR>
&nbsp;&nbsp;&nbsp;Color randomColors[];<BR>
&nbsp;&nbsp;&nbsp;// This is the data for the display..<BR>
&nbsp;&nbsp;&nbsp;GraphData gd;<BR>
&nbsp;&nbsp;&nbsp;// Maximum scale of graph...<BR>
&nbsp;&nbsp;&nbsp;int maxValue;<BR>
<BR>
&nbsp;&nbsp;&nbsp;// Constructor just inits data...<BR>
&nbsp;&nbsp;&nbsp;public GraphCanvas() {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;gd = null;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Store the random colors...
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;randomColors = new Color[6];
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;randomColors[0] = Color.yellow;
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;randomColors[1] = Color.red;
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;randomColors[2] = Color.green;
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;randomColors[3] = Color.magenta;
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;randomColors[4] = Color.cyan;
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;randomColors[5] = Color.blue;
<BR>
&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;// Set up graphics display...<BR>
&nbsp;&nbsp;&nbsp;void prepareNewGraph(GraphData gphData,int graphMode)
{<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Store the data and string
values...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;gd = gphData;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;this.graphMode = graphMode;
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// First calculate maximum
value of graph...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;maxValue = calculateMaxValue();
<BR>
&nbsp;&nbsp;&nbsp;}<BR>
<BR>
&nbsp;&nbsp;&nbsp;// Calculate the maximum value of the graph...
<BR>
&nbsp;&nbsp;&nbsp;int calculateMaxValue() {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;double maximum = 0.0;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;double data;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int temp,roundMax;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// First get maximum figure...
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int length = gd.size();<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;for (int i = 0; i &lt; length;
++i) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;data = gd.getData(i);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if (data
&gt; maximum)<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;maximum
= data;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;} // end for<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Now round it up to nearest
power of 10<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;roundMax = 1;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;for (temp = (int)maximum;temp
&gt; 0; temp /= 10)<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;roundMax
*= 10;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return roundMax;<BR>
&nbsp;&nbsp;&nbsp;}<BR>
<BR>
<BR>
&nbsp;&nbsp;&nbsp;//&nbsp;&nbsp;Draw the graph...<BR>
&nbsp;&nbsp;&nbsp;public synchronized void paint (Graphics g)
{<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if (gd == null)<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return;
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Dimension dm = size();<BR>
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Calculate margins...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int height = g.getFontMetrics().getHeight();
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int ymargin = 3 * height;
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int xmargin = g.getFontMetrics().stringWidth(&quot;1112345.67&quot;);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int length = gd.size();<BR>
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Select bottom-left origin
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Point origin = new Point(xmargin,dm.height
- ymargin);<BR>
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Draw X-Axis line<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int endx = dm.width - xmargin;
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;g.drawLine(origin.x,origin.y,endx,origin.y);
<BR>
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Draw Y-Axis line<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;g.drawLine(origin.x,ymargin,origin.x,origin.y);
<BR>
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Calculate how headers are
spread out...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int yIncrement = (origin.y
- ymargin)/10;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int xIncrement = (endx - origin.x)
/ (length + 1);<BR>
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Draw horizontal axis headers
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int i,x;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int yMarkStart = origin.y
+ height;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int yTextStart = yMarkStart
+ height;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;for (i = 1; i &lt; (length
+ 1); ++i) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Draw
marker...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;x = origin.x
+ (xIncrement * i);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;g.drawLine(x,yMarkStart,x,origin.y);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Print
value header...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;g.drawString(gd.getHeading(i
- 1),x,yTextStart);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Draw vertical axis headers...
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int y;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int inset = g.getFontMetrics().charWidth('W');
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int xMarkStart = origin.x
- inset;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int xTextStart = inset;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int dataIncrement = maxValue
/ 10;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;String yHeader;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;for (i = 0; i &lt;= 10; ++i)
{<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Draw
marker...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;y = origin.y
- (i * yIncrement);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;g.drawLine(xMarkStart,y,origin.x,y);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Print
increment header...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;yHeader
= String.valueOf(dataIncrement * i);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;g.drawString(yHeader,xTextStart,y);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Call Graphic specific drawing..
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int vertLength = origin.y
- ymargin;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;double dbLen = (double)randomColors.length;
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int index;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;int rectOffset = xIncrement
/ 2; // For bar graphs...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Point lastPt = null;<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;for (i = 1; i &lt; (length
+ 1); ++i) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Plot
points, connecting points with lines...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;x = origin.x
+ (xIncrement * i);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;y = origin.y
- (int)((gd.getData(i - 1)/maxValue) * vertLength);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Randomize
colors...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;index =
(int)(dbLen * Math.random());<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;g.setColor(randomColors[index]);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// If line
graph, draw connecting lines...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if (graphMode
== LINE_GRAPH) {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if
(lastPt != null)<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;g.drawLine(lastPt.x,lastPt.y,x,y);
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;lastPt
= new Point(x,y);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;// Otherwise,
bar graph draw rectangle...<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;else {<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;g.fillRect(x
- rectOffset,y,xIncrement,origin.y - y);<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}<BR>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;} // end for<BR>
&nbsp;&nbsp;&nbsp;}<BR>
}</TT>
</BLOCKQUOTE>
<HR>
<P>
After the maximum value is determined, the graph is ready to be
painted. This is surprisingly easy. The first step is to get the
dimensions of the canvas area and to figure where the bottom-left
origin of the graph should be; this is where the vertical line
that marks the range of values and the horizontal line that provides
the column headers will meet. The margins allow room at the sides
and the bottom for displaying the range and column headers. These
are calculated through the use of the FontMetrics class's <TT>getHeight()</TT>
and <TT>stringWidth()</TT> methods.
These margins make it easy to calculate the operations that follow.
The next step is drawing the vertical and horizontal lines from
the origin to the appropriate margin.
<P>
The column headers are next drawn underneath the horizontal line.
The location of the headers is based on the length of the line
divided by the number of columns. The horizontal range of values
is calculated similarly, except that the locations are based on
dividing the maximum value by ten and incrementing accordingly.
The range values and headers are drawn through the <TT>drawString()</TT>
method. The nearby <TT>drawLine()</TT>
methods are used to make a small line marker indicating the range
or header position.
<P>
The last step is to plot the graph. This is done in a <TT>for</TT>
loop that moves across each column of data. For each column, a
random color is chosen for the ensuing graph figure. This is done
by using the <TT>Math.random()</TT>
method, which returns a number between 0.0 and 1.0. The color
is then set by calling the Graphics object's <TT>setColor()</TT>
method. The data is then plotted based on its position in relation
to the origin and the maximum value. If it is a line graph, a
line is drawn from the endpoint of the last line drawn to the
new value; the <TT>drawLine()</TT>
method is used to do this. If it is a bar graph, a rectangle is
drawn from the horizontal baseline to the plotted value with the
<TT>fillRect()</TT> method of the
Graphics class. Both the line and the interior of the bar rectangle
will be the color just set by the random procedure.
<H2><A NAME="Summary"><FONT SIZE=5 COLOR=#FF0000>Summary</FONT></A>
</H2>
<P>
This concludes the development of the spreadsheet applet. By going
through this part of the book, you have learned most of the fundamental
techniques needed to use the AWT package. You have also been exposed
to exception handling, as well as the underlying principles of
using input/output streams.
<P>
The next step is to tie these techniques in with some of Java's
more advanced features, such as multithreading and sockets programming.
With a good understanding of these new techniques, you can produce
a network-enabled applet ready for prime-time use on the Internet!
<P>
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