| << Chapter < Page | Chapter >> Page > |
Following this, the constructor accesses the variables named frameWidth and frameHeight belonging to the enclosing PlotALot01 object and uses those values to set the size of the Page .
Then the constructor accesses the title and pageCounter variables belonging to the enclosing PlotALot01 object and uses those values to set the title for the Page object.
Finally, the code in Listing 19 causes the Page object to become visible on the screen.
Still inside the constructor, Listing 20 instantiates an object of an anonymous inner class to terminate the program when the user clicks on the close button on the Page (the X-button in the upper-right corner) .
(In case you are unfamiliar with anonymous inner classes, see my module titled The Essence of OOP using Java, Anonymous Classes .)
| Listing 20. An anonymous terminator for the Page class. |
|---|
addWindowListener(
new WindowAdapter(){public void windowClosing(
WindowEvent e){System.exit(0);//terminate program
}//end windowClosing()}//end WindowAdapter
);//end addWindowListener}//end constructor |
Listing 20 also signals the end of the constructor for the Page class.
This method, which is shown in its entirety in Listing 21 , receives a sample value of type double and also receives the sample counter associated with that data value. It uses the value of the sample counter to store the data value inan array object belonging to the MyCanvas object.
| Listing 21. The putData method of the Page class. |
|---|
void putData(double sampleValue,
int sampleCounter){canvas.data[sampleCounter] = sampleValue;this.sampleCounter = sampleCounter;
}//end putData |
In addition, the putData method saves the sample counter value in an instance variable to make it available to the overridden paint method later. This value is needed by the paint method so it will know how many samples to plot on the final page which probablywon't be full.
The MyCanvas class, which begins in Listing 22 , is a member class of the Page class. As such, methods belonging to an object of the MyCanvas class have directaccess to the other members of the enclosing Page object, including instance variables of the Page object. In addition, methods belonging to an object of theMyCanvas class have direct access to the other members, including instance variables, of the enclosing PlotALot01 object.
| Listing 22. Beginning of the MyCanvas class. |
|---|
class MyCanvas extends Canvas{
double []data =
new double[samplesPerPage]; |
This class definition begins by creating a new array object of type double that will be used to store the data values belonging to the page. The size of the array is specified by the value of samplesPerPage .
The overridden paint method of the MyCanvas class begins in Listing 23 .
| Listing 23. Beginning of the overridden paint method. |
|---|
public void paint(Graphics g){
for(int cnt = 0;cnt<tracesPerPage;
cnt++){g.drawLine(0,
(cnt+1)*traceSpacing,this.getWidth(),
(cnt+1)*traceSpacing);}//end for loop |
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