Design Patterns Java™ Workbook

Chapter 27. Decorator

Figure 27.4. The FunPanel class accepts x and y functions to plot.

The setXY() method in the FunPanel class accepts x and y functions and calculates
the minimum and maximum values of these curves:

public void setXY(Function fx, Function fy)
{
this.fx = fx;
this.fy = fy;
calculateExtrema();
repaint();
}

The functions that the setXY() method accepts are parametric functions of time. Any code
that works with the curve of a function will evaluate the function as time varies from 0 to 1.
We shall see that this approach will let us plot parabolas, circles, and other types of curves for
which y is not strictly a function of x. The idea that time varies from 0 to 1 appears several
places in the function-plotting code, such as the calculation of the extreme values of the
functions: