fill41.java

JAVA编程思想第四版英文原版习题答案. pdf原版的

// generics/Fill41.java
// TIJ4 Chapter Generics, Exercise 41, page 737
// Modify Fill2.java to use the classes in typeinfo.pets instead
// of the Coffee classes.
// Using adapters to simulate latent typing.
// {main: Fill41Test}
import typeinfo.pets.*;
import java.util.*;
import net.mindview.util.*;
import static net.mindview.util.Print.*;

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

public class Fill41 {
	// 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(Exception e) {
				throw new RuntimeException(e);
			}
	}
	// Generator version:
	public static <T> void fill(Addable<T> addable, 
	Generator<T> generator, int size) {
		for(int i = 0; i < size; i++)
			addable.add(generator.next());
	}
}

// To adapt a base type, your 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;
	}
	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<T>(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> {
	public void add(T item) { super.add(item); }
}

class Fill41Test {
	public static void main(String[] args) {
		// Adapt a collection:
		List<Pet> pets = new ArrayList<Pet>();
		Fill41.fill(
			new AddableCollectionAdapter<Pet>(pets),
			Pet.class, 3);
		// Helper method captures the type:
		Fill41.fill(Adapter.collectionAdapter(pets), Manx.class, 2);
		for(Pet p : pets) print(p);
		print("---------------");
		// Use an adapted class:
		AddableSimpleQueue<Pet> petQueue = 
			new AddableSimpleQueue<Pet>();
		Fill41.fill(petQueue, Pug.class, 4);
		Fill41.fill(petQueue, Gerbil.class, 1);
		for(Pet p : petQueue) print(p);		
	}
}