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| Listing 22. Array to hold Canvas objects. |
|---|
//Create array to hold correct
// number of Canvas objects.canvases =
new Canvas[data.getNmbr()];
//Throw exception if number of// functions is greater than 5.
number = data.getNmbr();if(number>5){
throw new NoSuchMethodException("Too many functions. "
+ "Only 5 allowed.");}//end if |
Although the limit could easily be increased, this program is currently limited to plotting the output from five functions. The code in Listing 22 checks this limit and throws an exception if an attempt is made to plot morethan five functions.
Although somewhat long and rather tedious, the code in Listing 23 is completely straightforward. This code continues with the construction of the GUIobject, creating text fields, a button, etc.
| Listing 23. Routine GUI construction code. |
|---|
//Create the control panel and
// give it a border for cosmetics.JPanel ctlPnl = new JPanel();
ctlPnl.setLayout(//?rows x 4 colsnew GridLayout(0,4));
ctlPnl.setBorder(new EtchedBorder());
//Button for replotting the graphJButton graphBtn =
new JButton("Graph");graphBtn.addActionListener(this);
//Populate each panel with a label// and a text field. Will place
// these panels in a grid on the// control panel later.
pan0.add(new JLabel("xMin"));pan0.add(xMinTxt);
pan1.add(new JLabel("xMax"));pan1.add(xMaxTxt);
pan2.add(new JLabel("yMin"));pan2.add(yMinTxt);
pan3.add(new JLabel("yMax"));pan3.add(yMaxTxt);
pan4.add(new JLabel("xTicInt"));pan4.add(xTicIntTxt);
pan5.add(new JLabel("yTicInt"));pan5.add(yTicIntTxt);
pan6.add(new JLabel("xCalcInc"));pan6.add(xCalcIncTxt);
//Add the populated panels and the// button to the control panel with
// a grid layout.ctlPnl.add(pan0);
ctlPnl.add(pan1);ctlPnl.add(pan2);
ctlPnl.add(pan3);ctlPnl.add(pan4);
ctlPnl.add(pan5);ctlPnl.add(pan6);
ctlPnl.add(graphBtn); |
Because of the routine nature of the code in Listing 23 , I will let the comments suffice as an explanation.
If you refer back to Figure 1 , you will see that from one to five Canvas objects are stacked vertically in the center of a frame.
This is accomplished by placing a JPanel object in the center of the frame, and setting the layout manager on the JPanel to GridLayout . The grid is defined as having one column and an unspecified number of rows. Then one Canvas object is placed in each cell of the grid, beginning at the top and working downward from the top,until the required number of Canvas objects have been placed in the grid.
This is accomplished by the code in Listing 24 .
| Listing 24. The Canvas objects. |
|---|
//Create a panel to contain the
// Canvas objects. They will be// displayed in a one-column grid.
JPanel canvasPanel = new JPanel();canvasPanel.setLayout(//?rows,1 col
new GridLayout(0,1));//Create a custom Canvas object for
// each function to be plotted and// add them to the one-column grid.
// Make background colors alternate// between white and gray.
for(int cnt = 0;cnt<number; cnt++){
switch(cnt){case 0 :
canvases[cnt]=
new MyCanvas(cnt);canvases[cnt].setBackground(Color.WHITE);
break;case 1 :
canvases[cnt]=
new MyCanvas(cnt);canvases[cnt].setBackground(Color.LIGHT_GRAY);
break;case 2 :
canvases[cnt]=
new MyCanvas(cnt);canvases[cnt].setBackground(Color.WHITE);
break;case 3 :
canvases[cnt]=
new MyCanvas(cnt);canvases[cnt].setBackground(Color.LIGHT_GRAY);
break;case 4 :
canvases[cnt]=
new MyCanvas(cnt);canvases[cnt].setBackground(Color.WHITE);
}//end switch//Add the object to the grid.canvasPanel.add(canvases[cnt]);}//end for loop |
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