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The code in Listing 23 draws a set of horizontal axes on the MyCanvas object, one for each trace that will be plotted on the object. These horizontalaxes are shown in Figure 1 and Figure 5 .
Listing 24 shows the beginning of the code that is used to plot the data values stored in the array that was created in Listing 22 .
| Listing 24. Beginning of code to plot the points. |
|---|
if(sampleCounter>0){
for(int cnt = 0;cnt<= sampleCounter;
cnt++){//Compute a vertical offset
int yOffset =(1 + cnt*(sampSpacing + 1)/
this.getWidth())*traceSpacing; |
Listing 24 begins by testing the value of the sample counter to make certain that there are some points to be plotted. If so, it enters a for loop to plot each data value stored in the array. Because it uses the value ofthe sample counter to terminate the for loop, only those data values that have been stored in the array object will be plotted, even if thearray object isn't full.
The data values in the array are to be plotted on one or more horizontal axeson the page. Therefore, it is necessary to first determine where on the page each data value is to be plotted. The code in Listing 24 uses various pieces of information to determine the vertical location of the axis against which eachdata value will be plotted.
The code in Listing 25 draws an oval centered on the sample value to mark the sample on the plot. It is best if the dimensions of the oval are evenlydivisible by 2 for centering purposes. Otherwise, the ovals may appear to be a little off center.
| Listing 25. Draw an oval. |
|---|
g.drawOval(cnt*(sampSpacing + 1)%
this.getWidth() - ovalWidth/2,yOffset - (int)data[cnt] - ovalHeight/2,ovalWidth,
ovalHeight); |
Normally vertical coordinates increase going down the screen in Java graphics. However, this isn't what most of us are accustomed to seeing when weplot data. We prefer to see increasing vertical coordinates going up the page. The code in Listing 25 reverses the sign on the data values to cause positive data values to be plotted above the axis and negative data values to be plottedbelow the axis. Increasing values go up. Decreasing values go down.
The code in Listing 26 connects the sample values with straight lines. Care is taken to avoid drawing a line from the last sample value on one trace to thefirst sample value on the next trace. That would really be ugly.
| Listing 26. Connect the points with straight lines. |
|---|
if(cnt*(sampSpacing + 1)%
this.getWidth()>=
sampSpacing + 1){g.drawLine(
(cnt - 1)*(sampSpacing + 1)%this.getWidth(),
yOffset - (int)data[cnt-1],
cnt*(sampSpacing + 1)%this.getWidth(),
yOffset - (int)data[cnt]);
}//end if}//end for loop
}//end if for sampleCounter>0
}//end overridden paint method}//end inner class MyCanvas
}//end inner class Page}//end class PlotALot01 |
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