J2SE 1.5 新功能特性：新的For循环(3)

2008-02-23 09:43:32来源：互联网阅读 ()

package java.lang;
import java.util.Iterator;
public interface Iterable<T> {
Iterator<T> iterator();
}

To implement this interface in Catalog, you must code an iterator method. This method must return an Iterator object that is bound to the Product type.

The Catalog class stores all of its Product objects in an ArrayList. The easiest way to provide an Iterator object to a client is to simply return the Iterator object from the products ArrayList itself. Here is the modified Catalog class:

class Catalog implements Iterable<Product> {
private List<Product> products = new ArrayList<Product>();
void add(Product product) {
products.add(product);
}
public Iterator<Product> iterator() {
return products.iterator();
}
}

Note that the Iterator, the List reference, and the ArrayList are all bound to the Product type.

Once you have implemented the java.lang.Iterable interface, client code can use the foreach loop. Here is a bit of example code:

Catalog catalog = new Catalog();
catalog.add(new Product("1", "pinto", new BigDecimal("4.99")));
catalog.add(new Product("2", "flounder", new BigDecimal("64.88")));
catalog.add(new Product("2", "cucumber", new BigDecimal("2.01")));
for (Product product: catalog)
product.discount(new BigDecimal("0.1"));
for (Product product: catalog)
System.out.println(product);

Summary

The foreach loop provides a simple, consistent solution for iterating arrays, collection classes, and even your own collections. It eliminates much of the repetitive code that you would otherwise require. The foreach loop eliminates the need for casting as well as some potential problems. The foreach loop is a nice new addition to Java that was long overdue. I greatly appreciate the added simplicity in my source code.