Declare A Class That Can Be Used To Represent A Quadrilateral

2. Declare a class called Quadrilateral that can be used to represent a quadrilateral. What instance variables are required? This class should include the following methods:

• Accessor and mutator methods. Notice that negative and zero lengths should not be accepted.
• A method called isParallelogram that returns a Boolean value indicating if the quadrilateral is a parallelogram.
• A method called isRectangle that indicates if the quadrilateral is a rectangle. This method should invoke the method isParallelogram and return a Boolean value.
• A method called isSquare that returns the Boolean value “true” if the quadrilateral is a square. This method should invoke the method isRectangle and return a Boolean value. URL...

import java.awt.Point;
public class Quadrilateral{
private Point p1, p2, p3, p4;
public Quadrilateral (Point p1, Point p2, Point p3, Point p4) {

this.p1 = p1;
this.p2 = p2;
this.p3 = p3;
this.p4 = p4;
}
}

that is all i got, my professor has never mentioned on anything about quadrilateral,and i have 0 knowledge about this.