面向对象多态实例

// polymorphism/rodent/Rodent9.java
// TIJ4 Chapter Polymorphism, Exercise 9, page 289
/* Create an inheritance hierarchy of Rodent:Mouse, Gerbil, Hamster, etc. In the
* base class, provide methods that are common to all Rodents, and override these
* in the derived classes to perform different behaviors depending on the
* specific type of Rodent. Create an array of Rodent, fill it with different
* specific types of Rodents, and call your base-class methods to see what
* happens.
*/
/* Solution includes, in same package:
* import java.util.*;
* public class RandomRodentGenerator {
* private Random rand = new Random();
* public Rodent next() {
*  switch(rand.nextInt(3)) {
*   default:
*   case 0: return new Mouse();
*   case 1: return new Rat();
*   case 2: return new Squirrel();
*  }
* }
* }
*/

package polymorphism.rodent;
import static org.greggordon.tools.Print.*;

class Rodent {
 private String name = "Rodent";
 protected void eat() { println("Rodent.eat()"); }
 protected void run() { println("Rodent.run()"); }
 protected void sleep() { println("Rodent.sleep()"); }
 public String toString() { return name; }
}

class Mouse extends Rodent {
 private String name = "Mouse";
 protected void eat() { println("Mouse.eat()"); }
 protected void run() { println("Mouse.run()"); }
 protected void sleep() { println("Mouse.sleep()"); }
 public String toString() { return name; }
}

class Rat extends Rodent {
 private String name = "Rat";
 protected void eat() { println("Rat.eat()"); }
 protected void run() { println("Rat.run()"); }
 protected void sleep() { println("Rat.sleep()"); }
 public String toString() { return name; }
}

class Squirrel extends Rodent {
 private String name = "Squirrel";
 protected void eat() { println("Squirrel.eat()"); }
 protected void run() { println("Squirrel.run()"); }
 protected void sleep() { println("Squirrel.sleep()"); }
 public String toString() { return name; }
}

public class Rodent9 {
 private static RandomRodentGenerator gen = new RandomRodentGenerator();
 public static void main(String[] args) {
  Rodent[] rodents = new Rodent[10];
  for(Rodent r : rodents) {
   r = gen.next();
   println(r + ": ");
   r.eat();
   r.run();
   r.sleep();
  }
 }
}