Learning Processing: A Beginner's Guide to Programming Images ...

434 Learning Processing
23.6
// Move
void run() {
x = x + xspeed;
y = y + yspeed;
}
// Fall down
void gravity() {
yspeed + = 0.1;
}
// Stop moving
void stop() {
xspeed = 0;
yspeed = 0;
}
// Ready for deletion
boolean finished() {
life – = 2.0;
if (life < 0) return true;
else return false;
}
// Show
void display() {
stroke(0);
fill(0,life);
ellipse(x,y,10,10);
}
}
Exercise 23-3: Write a Button class that includes a Rectangle object to determine if the
mouse has clicked inside the button’s area. (Th is is an extension of Exercise 9-8 .)
Exception (Error) Handling
In addition to a very large library of useful classes, the Java programming language includes some features
beyond what we have covered while learning Processing . We will explore one of those features now:
exception handling .
Programming mistakes happen. We have all seen them.
java.lang.ArrayIndexOutOfBoundsException
java.io.IOException: openStream() could not open file.jpg
java.lang.NullPointerException
The Particle has a “life” variable which
decreases. When it reaches 0 the Particle
can be removed from the ArrayList.