The Java Language Specification, Third Edition

15.12.4 Runtime Evaluation of Method Invocation EXPRESSIONS
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15.12.4.8 Example: Overriding
In the example:
class Point {
final int EDGE = 20;
int x, y;
void move(int dx, int dy) {
x += dx; y += dy;
if (Math.abs(x) >= EDGE || Math.abs(y) >= EDGE)
clear();
}
void clear() {
System.out.println("\tPoint clear");
x = 0; y = 0;
}
}
class ColoredPoint extends Point {
int color;
void clear() {
System.out.println("\tColoredPoint clear");
super.clear();
color = 0;
}
}
the subclass ColoredPoint extends the clear abstraction defined by its superclass
Point. It does so by overriding the clear method with its own method,
which invokes the clear method of its superclass, using the form super.clear.
This method is then invoked whenever the target object for an invocation of
clear is a ColoredPoint. Even the method move in Point invokes the clear
method of class ColoredPoint when the class of this is ColoredPoint, as
shown by the output of this test program:
class Test {
public static void main(String[] args) {
Point p = new Point();
System.out.println("p.move(20,20):");
p.move(20, 20);
ColoredPoint cp = new ColoredPoint();
System.out.println("cp.move(20,20):");
cp.move(20, 20);
p = new ColoredPoint();
System.out.println("p.move(20,20), p colored:");
p.move(20, 20);
DRAFT