OnJava8-Examples/generics/Fill2.java

// generics/Fill2.java
// <20>2016 MindView LLC: see Copyright.txt
// Using adapters to simulate latent typing.
// {main: Fill2Test}
import generics.coffee.*;
import java.util.*;
import java.util.function.*;

interface Addable<T> { void add(T t); }

public class Fill2 {
  // Classtoken version:
  public static <T> void fill(Addable<T> addable,
  Class<? extends T> classToken, int size) {
    for(int i = 0; i < size; i++)
      try {
        addable.add(classToken.newInstance());
      } catch(InstantiationException |
              IllegalAccessException e) {
        throw new RuntimeException(e);
      }
  }
  // Supplier version:
  public static <T> void fill(Addable<T> addable,
    Supplier<T> generator, int size) {
    for(int i = 0; i < size; i++)
      addable.add(generator.get());
  }
}

// To adapt a base type, you must use composition.
// Make any Collection Addable using composition:
class AddableCollectionAdapter<T> implements Addable<T> {
  private Collection<T> c;
  public AddableCollectionAdapter(Collection<T> c) {
    this.c = c;
  }
  @Override
  public void add(T item) { c.add(item); }
}

// A Helper to capture the type automatically:
class Adapter {
  public static <T>
  Addable<T> collectionAdapter(Collection<T> c) {
    return new AddableCollectionAdapter<>(c);
  }
}

// To adapt a specific type, you can use inheritance.
// Make a SimpleQueue Addable using inheritance:
class AddableSimpleQueue<T>
extends SimpleQueue<T> implements Addable<T> {
  @Override
  public void add(T item) { super.add(item); }
}

class Fill2Test {
  public static void main(String[] args) {
    // Adapt a Collection:
    List<Coffee> carrier = new ArrayList<>();
    Fill2.fill(
      new AddableCollectionAdapter<>(carrier),
      Coffee.class, 3);
    // Helper method captures the type:
    Fill2.fill(Adapter.collectionAdapter(carrier),
      Latte.class, 2);
    for(Coffee c: carrier)
      System.out.println(c);
    System.out.println("----------------------");
    // Use an adapted class:
    AddableSimpleQueue<Coffee> coffeeQueue =
      new AddableSimpleQueue<>();
    Fill2.fill(coffeeQueue, Mocha.class, 4);
    Fill2.fill(coffeeQueue, Latte.class, 1);
    for(Coffee c: coffeeQueue)
      System.out.println(c);
  }
}
/* Output:
Coffee 0
Coffee 1
Coffee 2
Latte 3
Latte 4
----------------------
Mocha 5
Mocha 6
Mocha 7
Mocha 8
Latte 9
*/