OnJava8-Examples/reflection/PetCounter3.java

// reflection/PetCounter3.java
// (c)2021 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// Using isInstance()
import java.util.*;
import java.util.stream.*;
import onjava.*;
import reflection.pets.*;

public class PetCounter3 {
  static class Counter extends
  HashMap<Class<? extends Pet>, Integer> {
    Counter() {
      super(PetCreator.ALL_TYPES.stream()
        .map(type -> Pair.make(type, 0))
        .collect(
          Collectors.toMap(Pair::key, Pair::value)));
    }
    public void count(Pet pet) {
      // Class.isInstance() eliminates instanceofs:
      entrySet().stream()
        .filter(pair -> pair.getKey().isInstance(pet))
        .forEach(pair ->
          put(pair.getKey(), pair.getValue() + 1));
    }
    @Override public String toString() {
      String result = entrySet().stream()
        .map(pair -> String.format("%s=%s",
          pair.getKey().getSimpleName(),
          pair.getValue()))
        .collect(Collectors.joining(", "));
      return "{" + result + "}";
    }
  }
  public static void main(String[] args) {
    Counter petCount = new Counter();
    new PetCreator().stream()
      .limit(20)
      .peek(petCount::count)
      .forEach(p -> System.out.print(
        p.getClass().getSimpleName() + " "));
    System.out.println("\n" + petCount);
  }
}
/* Output:
Rat Manx Cymric Mutt Pug Cymric Pug Manx Cymric Rat
EgyptianMau Hamster EgyptianMau Mutt Mutt Cymric Mouse
Pug Mouse Cymric
{EgyptianMau=2, Mouse=2, Pet=20, Cymric=5, Rat=2,
Dog=6, Mutt=3, Hamster=1, Cat=9, Manx=7, Rodent=5,
Pug=3}
*/