A void method is a method that performs some function but does not return a value.
Examples:
// this code segment assumes that slope is an instance variable
// and is of type double
public void calculateSlope(int x1, int y1, int x2, int y2)
{
if (x1 != x2)
{
slope = (double)(y2-y1)/(x2-x1);
}
}