Mega Code Archive
Polymorphism in Java
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// : c07:Shapes.java
// Polymorphism in Java.
// From 'Thinking in Java, 3rd ed.' (c) Bruce Eckel 2002
// www.BruceEckel.com. See copyright notice in CopyRight.txt.
import java.util.Random;
class Shape {
void draw() {
}
void erase() {
}
}
class Circle extends Shape {
void draw() {
System.out.println("Circle.draw()");
}
void erase() {
System.out.println("Circle.erase()");
}
}
class Square extends Shape {
void draw() {
System.out.println("Square.draw()");
}
void erase() {
System.out.println("Square.erase()");
}
}
class Triangle extends Shape {
void draw() {
System.out.println("Triangle.draw()");
}
void erase() {
System.out.println("Triangle.erase()");
}
}
// A "factory" that randomly creates shapes:
class RandomShapeGenerator {
private Random rand = new Random();
public Shape next() {
switch (rand.nextInt(3)) {
default:
case 0:
return new Circle();
case 1:
return new Square();
case 2:
return new Triangle();
}
}
}
public class ShapesDemo {
private static RandomShapeGenerator gen = new RandomShapeGenerator();
public static void main(String[] args) {
Shape[] s = new Shape[9];
// Fill up the array with shapes:
for (int i = 0; i < s.length; i++)
s[i] = gen.next();
// Make polymorphic method calls:
for (int i = 0; i < s.length; i++)
s[i].draw();
}
} ///:~
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