Add the following accessor method to your Line class:

public boolean isCollinear(Point p)

Returns true if the given Point is collinear with the Points of this Line—that is, if, when this Line is stretched infinitely, it would eventually hit the given Point. Points are collinear if a straight line can be drawn that connects them. Two basic examples are three points that have the same -x or -y coordinate. The more general case can be determined by calculating the slope of the line between each pair of points and checking whether this slope is the same for all pairs of points. Use the formula (y₂ − y₁) / (x₂ − x₁) to determine the slope between two point (x₁, y₁) and (x₂, y₂). Since Java’s double type is imprecise, round all slope values to a reasonable accuracy such as four digits past the decimal point before you compare them.