petcount.java

中文JAVA编程思想第二版,一本很好的JAVA入门书籍!

//: c12:PetCount.java
// From 'Thinking in Java, 2nd ed.' by Bruce Eckel
// www.BruceEckel.com. See copyright notice in CopyRight.txt.
// Using instanceof.
import java.util.*;

public class PetCount {
  static String[] typenames = {
    "Pet", "Dog", "Pug", "Cat",
    "Rodent", "Gerbil", "Hamster",
  };
  // Exceptions thrown out to console:
  public static void main(String[] args) 
  throws Exception {
    ArrayList pets = new ArrayList();
    try {
      Class[] petTypes = {
        Class.forName("Dog"),
        Class.forName("Pug"),
        Class.forName("Cat"),
        Class.forName("Rodent"),
        Class.forName("Gerbil"),
        Class.forName("Hamster"),
      };
      for(int i = 0; i < 15; i++)
        pets.add(
          petTypes[
            (int)(Math.random()*petTypes.length)]
            .newInstance());
    } catch(InstantiationException e) {
      System.err.println("Cannot instantiate");
      throw e;
    } catch(IllegalAccessException e) {
      System.err.println("Cannot access");
      throw e;
    } catch(ClassNotFoundException e) {
      System.err.println("Cannot find class");
      throw e;
    }
    HashMap h = new HashMap();
    for(int i = 0; i < typenames.length; i++)
      h.put(typenames[i], new Counter());
    for(int i = 0; i < pets.size(); i++) {
      Object o = pets.get(i);
      if(o instanceof Pet)
        ((Counter)h.get("Pet")).i++;
      if(o instanceof Dog)
        ((Counter)h.get("Dog")).i++;
      if(o instanceof Pug)
        ((Counter)h.get("Pug")).i++;
      if(o instanceof Cat)
        ((Counter)h.get("Cat")).i++;
      if(o instanceof Rodent)
        ((Counter)h.get("Rodent")).i++;
      if(o instanceof Gerbil)
        ((Counter)h.get("Gerbil")).i++;
      if(o instanceof Hamster)
        ((Counter)h.get("Hamster")).i++;
    }
    for(int i = 0; i < pets.size(); i++)
      System.out.println(pets.get(i).getClass());
    for(int i = 0; i < typenames.length; i++)
      System.out.println(
        typenames[i] + " quantity: " +
        ((Counter)h.get(typenames[i])).i);
  }
} ///:~