Polymorphism (Part 2)
Fattane Zarrinkalam
Why Polymorphism?
2
Paint Program
3
Inheritance Hierarchy
Shape
- position
+ getPosition()
+ draw()
+ getArea()
Circle
- radius
+ getRadius()
+ draw()
+ getArea()
Rectangle
- length
- width
+
+
+
+
getLength()
getWidth()
draw()
getArea()
4
Paint Program
• Let’s develop two versions of Paint program
• Without polymorphism
• With polymorphism
5
Paint Program
• Let’s develop two versions of Paint program
• Without polymorphism
• With polymorphism
6
Paint Program – Without Polymorphism
Circle[] circles = new Circle[100];
Rectangle[] rectangles = new Rectangle[100];
int circlesCount = 0, rectanglesCount = 0;
loop:
while(true) {
showMenu();
int choice = readUserChoice();
switch (choice) {
case 0: break loop;
case 1: circles[circlesCount++] = new Circle();
break;
case 2: rectangles[rectanglesCount++] = new Rectangle();
break;
}
}
for(Circle circle: circles)
circle.draw();
for(Rectangle rectangle: rectangles)
rectangle.draw();
7
Paint Program – Without Polymorphism
Circle[] circles = new Circle[100];
Rectangle[] rectangles = new Rectangle[100];
A separate array for each type of
shape
8
Paint Program – Without Polymorphism
Circle[] circles = new Circle[100];
Rectangle[] rectangles = new Rectangle[100];
A separate array for each type of
shape
int circlesCount = 0, rectanglesCount = 0;
loop:
while(true) {
A separate counter for each type of
showMenu();
shape
int choice = readUserChoice();
A separate case for each type of shape
switch (choice) {
case 0: break loop;
case 1: circles[circlesCount++] = new Circle();
break;
case 2: rectangles[rectanglesCount++] = new Rectangle();
break;
}
}
9
Paint Program – Without Polymorphism
Circle[] circles = new Circle[100];
Rectangle[] rectangles = new Rectangle[100];
A separate array for each type of
shape
int circlesCount = 0, rectanglesCount = 0;
loop:
while(true) {
A separate counter for each type of
showMenu();
shape
int choice = readUserChoice();
A separate case for each type of shape
switch (choice) {
case 0: break loop;
case 1: circles[circlesCount++] = new Circle();
break;
case 2: rectangles[rectanglesCount++] = new Rectangle();
break;
}
}
for(Circle circle: circles)
circle.draw();
A separate loop for processing every type of
shape
for(Rectangle rectangle: rectangles)
rectangle.draw();
10
Paint Program
• Let’s develop two versions of Paint program
• Without polymorphism
• With polymorphism
11
Paint Program – With Polymorphism
Shape[] shapes = new Shape[200];
int shapesCount = 0;
loop:
while(true) {
showMenu();
int choice = readUserChoice();
switch (choice) {
case 0: break loop;
case 1: shapes[shapesCount++] = new Circle();
break;
case 2: shapes[shapesCount++] = new Rectangle();
break;
}
}
for(Shape shape: shapes)
shape.draw();
12
Paint Program – With Polymorphism
Shape[] shapes = new Shape[200];
A single array for all different types of
shapes
13
Paint Program – With Polymorphism
Shape[] shapes = new Shape[200];
A single array for all different types of
shapes
int shapesCount = 0;
A single counter for all different types of
loop:
shapes
while(true) {
A separate case for each type of shape
showMenu();
int choice = readUserChoice();
switch (choice) {
case 0: break loop;
case 1: shapes[shapesCount++] = new Circle();
break;
case 2: shapes[shapesCount++] = new Rectangle();
break;
}
}
14
Paint Program – With Polymorphism
Shape[] shapes = new Shape[200];
A single array for all different types of
shapes
int shapesCount = 0;
A single counter for all different types of
loop:
shapes
while(true) {
A separate case for each type of shape
showMenu();
int choice = readUserChoice();
switch (choice) {
case 0: break loop;
case 1: shapes[shapesCount++] = new Circle();
break;
case 2: shapes[shapesCount++] = new Rectangle();
break;
}
}
for(Shape shape: shapes)
shape.draw();
A single loop for processing over different
types of shapes
15
Real World Scale!
• What if we have tens of types of shapes?
• Extendibility
16
Inheritance Hierarchy
Shape
- position
+ getPosition()
+ draw()
+ getArea()
Circle
- radius
+ getRadius()
+ draw()
+ getArea()
Rectangle
- length
- width
+
+
+
+
getLength()
getWidth()
draw()
getArea()
Square
- side
+ getSide()
+ draw()
+ getArea()
17
Paint Program – Without Polymorphism
Circle[] circles = new Circle[100];
Rectangle[] rectangles = new Rectangle[100];
Square[] squares = new Square[100];
18
Paint Program – Without Polymorphism
Circle[] circles = new Circle[100];
Rectangle[] rectangles = new Rectangle[100];
Square[] squares = new Square[100];
int circlesCount = 0, rectanglesCount = 0, squaresCount = 0;
loop:
while(true) {
showMenu();
int choice = readUserChoice();
switch (choice) {
case 0: break loop;
case 1: circles[circlesCount++] = new Circle();
break;
case 2: rectangles[rectanglesCount++] = new Rectangle();
break;
case 3: squares[squaresCount++] = new Square();
break;
}
}
19
Paint Program – Without Polymorphism
Circle[] circles = new Circle[100];
Rectangle[] rectangles = new Rectangle[100];
Square[] squares = new Square[100];
int circlesCount = 0, rectanglesCount = 0, squaresCount = 0;
loop:
while(true) {
showMenu();
int choice = readUserChoice();
switch (choice) {
case 0: break loop;
case 1: circles[circlesCount++] = new Circle();
break;
case 2: rectangles[rectanglesCount++] = new Rectangle();
break;
case 3: squares[squaresCount++] = new Square();
break;
}
}
for(Circle circle: circles) circle.draw();
for(Rectangle rectangle: rectangles) rectangle.draw();
for(Square square: squares) square.draw();
20
Paint Program – With Polymorphism
Shape[] shapes = new Shape[300];
21
Paint Program – With Polymorphism
Shape[] shapes = new Shape[300];
int shapesCount = 0;
loop:
while(true) {
showMenu();
int choice = readUserChoice();
switch (choice) {
case 0: break loop;
case 1: shapes[shapesCount++] = new Circle();
break;
case 2: shapes[shapesCount++] = new Rectangle();
break;
case 3: shapes[shapesCount++] = new Square();
break;
}
}
22
Paint Program – With Polymorphism
Shape[] shapes = new Shape[300];
int shapesCount = 0;
loop:
while(true) {
showMenu();
int choice = readUserChoice();
switch (choice) {
case 0: break loop;
case 1: shapes[shapesCount++] = new Circle();
break;
case 2: shapes[shapesCount++] = new Rectangle();
break;
case 3: shapes[shapesCount++] = new Square();
break;
}
}
for(Shape shape: shapes)
shape.draw();
23
• Consider a project that you have
done previously:
• Think about how inheritance and
polymorphism can be applied in
that project.
• Implement the improved version
of the code after applying
polymorphism.
24