【ThinkingInJava】29、对类进行计数

来源：互联网发布：网站域名备案注册证书编辑：程序博客网时间：2024/06/06 17:11

<pre name="code" class="java">//: typeinfo/pets/PetCreator.java// Creates random sequences of Pets.package Lesson14TypeInformation.pets;import java.util.*;public abstract class PetCreator {  private Random rand = new Random(47);  // The List of the different types of Pet to create:  public abstract List<Class<? extends Pet>> types();  public Pet randomPet() { // Create one random Pet    int n = rand.nextInt(types().size());    try {      return types().get(n).newInstance();    } catch(InstantiationException e) {      throw new RuntimeException(e);    } catch(IllegalAccessException e) {      throw new RuntimeException(e);    }  }  public Pet[] createArray(int size) {    Pet[] result = new Pet[size];    for(int i = 0; i < size; i++)      result[i] = randomPet();    return result;  }  public ArrayList<Pet> arrayList(int size) {    ArrayList<Pet> result = new ArrayList<Pet>();    Collections.addAll(result, createArray(size));    return result;  }} ///:~

//: typeinfo/pets/ForNameCreator.javapackage Lesson14TypeInformation.pets;import java.util.*;public class ForNameCreator extends PetCreator {  private static List<Class<? extends Pet>> types =    new ArrayList<Class<? extends Pet>>();  // Types that you want to be randomly created:  private static String[] typeNames = {    "Lesson14TypeInformation.pets.Mutt",    "Lesson14TypeInformation.pets.Pug",    "Lesson14TypeInformation.pets.EgyptianMau",    "Lesson14TypeInformation.pets.Manx",    "Lesson14TypeInformation.pets.Cymric",    "Lesson14TypeInformation.pets.Rat",    "Lesson14TypeInformation.pets.Mouse",    "Lesson14TypeInformation.pets.Hamster"  };  @SuppressWarnings("unchecked")  private static void loader() {    try {      for(String name : typeNames)        types.add(          (Class<? extends Pet>)Class.forName(name));    } catch(ClassNotFoundException e) {      throw new RuntimeException(e);    }  }  static { loader(); }  public List<Class<? extends Pet>> types() {return types;}} ///:~

/*** 书本:《Thinking In Java》* 功能:为了对pet进行计数，我们做一个能跟踪各种不同类型的Pet的数量的工具，用map* 文件:PetCount.java* 时间:2015年4月13日17:25:39* 作者:cutter_point*/package Lesson14TypeInformation;import java.util.HashMap;import Lesson14TypeInformation.pets.*;import static net.mindview.util.Print.*;public class PetCount {static class PetCounter extends HashMap<String, Integer>{public void count(String type)//添加一个pet{Integer quantity = this.get(type);if(quantity == null)//如果没有那么就变为1this.put(type, 1);else//如果有，那么就在基础上加一个this.put(type, quantity+1);}}public static void countPets(PetCreator creator){PetCounter counter = new PetCounter();for(Pet pet : creator.createArray(20)){printnb(pet.getClass().getSimpleName() + " ");if(pet instanceof Pet)//判断是不是这个类counter.count("Pet");if(pet instanceof Dog)counter.count("Dog");if(pet instanceof Mutt)counter.count("Mutt");if(pet instanceof Pug)counter.count("Pug");if(pet instanceof Cat)counter.count("Cat");if(pet instanceof Manx)counter.count("EgyptianMau");if(pet instanceof Manx)counter.count("Manx");if(pet instanceof Manx)counter.count("Cymric");if(pet instanceof Rodent)counter.count("Rodent");if(pet instanceof Rat)counter.count("Rat");if(pet instanceof Mouse)counter.count("Mouse");if(pet instanceof Hamster)counter.count("Hamster");}print();print(counter);}public static void main(String[] args) {countPets(new ForNameCreator());}}

前面的那两个帮助类是为了产生一些pet类，而pet类的格式是：

//: typeinfo/pets/Cat.javapackage Lesson14TypeInformation.pets;public class Cat extends Pet {  public Cat(String name) { super(name); }  public Cat() { super(); }} ///:~

输出：

Rat -obj2 Manx -obj2 Cymric -obj2 Mutt -obj2 Pug -obj2 Cymric -obj2 Pug -obj2 Manx -obj2 Cymric -obj2 Rat -obj2 EgyptianMau -obj2 Hamster -obj2 EgyptianMau -obj2 Mutt -obj2 Mutt -obj2 Cymric -obj2 Mouse -obj2 Pug -obj2 Mouse -obj2 Cymric -obj2
{Rat=2, Cymric=7, Cat=9, Pet=20, Dog=6, Manx=7, EgyptianMau=7, Pug=3, Mouse=2, Rodent=5, Hamster=1, Mutt=3} obj1

0 0