Description
Objectives
• Introduction to interfaces
• Introduction to abstract data types
Part I – Interfaces
1. Download all of the provided lab files to your Lab3 working directory.
We are going to use an interface to specify what a Shape class should look like. As depicted in the UML
diagram below, a Shape should have methods for calculating area, calculating perimeter and determining
whether a given Point lies with in a Shape. An interface does not include the implementation of these
methods, only their signatures and documentation. The implementation details of these method is
dependent on the type of Shape and therefore will be defined in the classes that implement the Shape
interface (ie. Circle, Rectangle)
2. Start by opening Shape.java to familiarize yourself with the method documentation.
The Circle and Rectangle classes implement the Shape interface (depicted by the dashed arrow between
them in the UML diagram below)
Circle and Rectangle both have an attribute of type Point (depicted by the solid line with no arrow
between them in the UML diagram below).
3. Open Circle.java and you will see a full implementation of the Circle class. Notice, it contains
implementations of all methods listed in Shape.java
Shape
<>
+ area(): double
+ perimeter(): double
+ contains(Point): boolean
+ toString(): String
Circle
– radius: int
– position: Point
+ Circle()
+ Circle(int)
+ Circle(int, Point)
+ area(): double
+ perimeter(): double
+ contains(Point): boolean
+ toString(): String
Rectangle
– length: int
– width: int
– position: Point
+ Rectangle()
+ Rectangle (int, int)
+ Rectangle (int, int, Point)
+ area(): double
+ perimeter(): double
+ contains(Point): boolean
+ toString(): String
Point
– x: int
– y: int
+ Point()
+ Point(int,int)
+ getX(): int
+ setX(int): void
+ getY(): int
+ setY(int): void
+ toString(): String
4. Begin the implementation of Rectangle.java
a. Create a new file that will be named Rectangle.java
b. Make the Rectangle class implement the Shape method. Look at the beginning of Circle.java
if you are unsure how to do this.
c. Try to compile Rectangle.java – You will see compile error something like this:
error: Rectangle is not abstract and does not override abstract method contains(Point) in
Shape
Fix this compile error by introducing stubs for each of the methods Rectangle must implement:
d. Copy the documentation and method signatures
from Shape.java to Rectangle.java
e. For each method signature:
i. remove the “;” from the end of the signature
ii. add an “{” and “}” to make it a method
iii. make the method public
iv. if the method that has a non-void return type, add a dummy return statement
For example, for the area method the stub would look like this:
public double area() {
return 0;
}
f. In the UML diagram on the previous page, notice that the Rectangle class has three fields:
length (which is type int), width (also type int), and position (type Point). Add these fields to
the Rectangle class.
g. The UML diagram on the previous page specifies three constructors for the Rectangle class.
Write the three constructors. Note: For the Rectangle class, we will assume the point is
in the bottom-left corner of the rectangle. This is important for the contains method you
will do later in the lab.
CHECKPOINT (Ungraded) – Now might be a good time to check-in with the TA if you are unclear of how to
proceed, or if you are unable to fix the compile errors in your program.
5. Complete the implementation of Rectangle.java
a. Open Lab3Tester.java and compile and run it. You will see tests failing.
b. Implement one method at a time, recompiling and rerunning the tester after each one
Part II – Using classes to define a data structure
We are now going to implement a class called ShapeList that will hold a collection of Shapes. The addition
of this class is depicted in our UML diagram:
1. Start by opening ShapeList.java Notice we have added the attributes, a blank constructor and
method stubs for you
a. Uncomment the call to testShapeList() in the main of Lab3Tester.java and compile/run it
b. Implement the constructor and each method one at a time.
2. Add tests to testShapeList() to ensure your add method has the correct behaviour when more than
2 elements are added to the list.
SUBMISSION (Graded) – Submit the ShapeList.java and Rectangle.java files into the Lab3 submission
page on ConneX.
Shape
<>
+ area(): double
+ perimeter(): double
+ contains(Point): boolean
+ toString(): String
Circle
– radius: int
– position: Point
+ Circle()
+ Circle(int)
+ Circle(int, Point)
+ area(): double
+ perimeter(): double
+ contains(Point): boolean
+ toString(): String
Rectangle
– length: int
– width: int
– position: Point
+ Rectangle()
+ Rectangle (int, int)
+ Rectangle (int, int, Point)
+ area(): double
+ perimeter(): double
+ contains(Point): boolean
+ toString(): String
Point
– x: int
– y: int
+ Point()
+ Point(int,int)
+ getX(): int
+ setX(int): void
+ getY(): int
+ setY(int): void
+ toString(): String
ShapeList
– elements: Shape[]
– count: int
+ add(Shape): void
+ size(): int
+ toString(): String
+ removeFront(): void
