thinking in java 14章

class Pet {
	String m_name;
	public Pet(String name) {
		m_name = name;
	}
	public Pet() {
		
	}
}

class Mutt extends Pet {
	public Mutt(String name) {
		super(name);
	}
	public Mutt(){}
}

class Pug extends Pet {
	public Pug(String name) { super(name); }
	public Pug(){}
}

class Manx extends Pet {
	public Manx(String name) { super(name); }
	public Manx(){}
}

abstract class PetCreator {
	Random rand = new Random();
	public abstract List<Class<? extends Pet>> types();
	
	public Pet randomPet() {
		int n = rand.nextInt(types().size());
		try {
		return types().get(n).newInstance();
		}
		catch(Exception e) {
			e.printStackTrace();
			return null;
		}
	}
	
	public Pet[] creatArray(int size) {
		Pet[] rst = new Pet[size];
		for (int i = 0; i < size; ++i)
			rst[i] = randomPet();
		return rst;
	}
}

class LiteralPetCreator extends PetCreator {
	
	static final List<Class<? extends Pet>> types = Arrays.asList(Mutt.class, Pug.class, Manx.class);
	static final List<Class<? extends Pet>> alltypes = Arrays.asList(Pet.class, Mutt.class, Pug.class, Manx.class);
	
	public List<Class<? extends Pet>> types(){
		return types;
	}
}

class PetCount3 {
	static class PetCounter extends LinkedHashMap<Class<? extends Pet>, Integer> {
		public PetCounter () {
			for( Class<? extends Pet> c: LiteralPetCreator.alltypes ) {
				put(c, 0);
			}
		}
		
		public void count(Pet pet) {
			for ( Map.Entry<Class<? extends Pet>, Integer> pair : entrySet()) {
				if(pair.getKey().isInstance(pet)) {
					put(pair.getKey(), pair.getValue() + 1);
				}
			}
		}
		
		public String toString() {
			StringBuilder sb = new StringBuilder("{");
			for( Map.Entry<Class<? extends Pet>, Integer> pair : entrySet()) {
				sb.append(pair.getKey().getSimpleName());
				sb.append("=");
				sb.append(pair.getValue());
				sb.append(", ");
			}
			sb.delete(sb.length()-2, sb.length());
			sb.append("}");
			return sb.toString();
		}
	}
}


public class tt {

	/**
	 * @param args
	 */
	
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		
		PetCount3.PetCounter cnt = new PetCount3.PetCounter();
		for (Pet p : new LiteralPetCreator().creatArray(20)) {
			System.out.print(p.getClass().getSimpleName() + " ");
			cnt.count(p);
		}
		System.out.println();
		System.out.println(cnt);
		
	}

}

Mutt Pug Mutt Mutt Manx Mutt Mutt Pug Mutt Mutt Mutt Mutt Pug Manx Manx Pug Pug Mutt Manx Mutt 
{Pet=20, Mutt=11, Pug=5, Manx=4}