The above example did not explain how to model the declaration of local variables. Recall that local variables may be introduced by statements like:
int a = (x + width)/2;
Polygon p = new Polygon();
Color cb = c.brighter();
To illustrate the handling of local variables, let's modify the Hole1 class to make its structure clearer.
import
java.awt.*;
import java.applet.Applet;
public class Hole2
extends Applet {
public void paint(Graphics g)
{
this.drawHole(g, 50);
this.drawHole(g, 25);
}
public void drawHole(Graphics g,
int rad) {
// Draw a yellow circle with radius rad at point (60,80) inscribed in a blue
square.
this.drawHoleAt(g, 60, 80, rad);
}
public void drawHoleAt(Graphics g,
int x, int y,
int rad) {
// Draw a yellow circle with radius rad at point (x,y) inscribed in a blue
square.
this.fillSquare(g, x-rad, y-rad, 2*rad, Color.blue);
this.fillCircle(g, x, y, rad, Color.yellow);
}
public void fillSquare(Graphics g,
int x, int y,
int side, Color clr) {
// Fill with color clr a square whose upper left corner is (x, y)
// and whose side length is side.
g.setColor(clr);
g.fillRect(x, y, side, side);
}
public void fillCircle(Graphics g,
int x, int y,
int rad, Color clr) {
// Fill with color clr a circle with center point (x, y) and radius rad.
int side = 2* rad;
g.setColor(clr);
g.fillOval(x-rad, y-rad, side, side);
}
}The above Hole2 class draws the same logo as the Hole1 class, but uses the extra methods drawHoleAt, fillSquare, and fillCircle. fillCircle uses the declaration int side = 2 * rad to introduce a local variable side that is twice the radius rad. When the red control dot encounters a declaration like this, it adds a new variable name side to the set of variables of the local execution frame for fillCircle.The execution tree that results from sending a paint message to Hole2 instance H2 with argument G2 is shown below in table form. Pay particular attention to the extra side variables in the frame for fillCircle.
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H2.paint(G2); |
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