Java Reference
In-Depth Information
The
ArrayList
is a very useful data structure that should normally be used in
place of the array type. It provides much more flexibility than a simple array, in that
elements can be added and removed dynamically with ease. While it is true that
Ar-
rayList
uses an array internally, you benefit from optimized
add()
and
re-
move()
operations that are implemented for you. Also,
ArrayList
implements
many other very useful methods. Refer to the online Java documentation for further de-
rayList.html
).
7-7. Making Your Objects Iterable
Problem
You have created a custom collection-based class that wraps (instead of extends) the
underlying collection type. Without exposing the internal implementation details of
your class, you would like objects of your class to be iterable, especially with the use
of a
foreach
statement.
Solution
Have your class extend the
Interable<T>
interface, where
T
is the element type of
the collection to be iterated. Implement the
iterator()
method to return the
Iter-
ator<T>
object from this collection. The example for this recipe is the
Stock-
Portfolio
class. Internally,
StockPortfolio
manages a collection of
Stock
objects. We would like users of our class to be able to treat
StockPortfolio
ob-
jects as iterable objects using a
foreach
statement. The
StockPortfolio
class
follows:
// See StockPortfolio.java and Stock.java
public class StockPortfolio implements Iterable<Stock> {
Map<String, Stock> portfolio = new HashMap<>();
public void add(Stock stock) {
portfolio.put(stock.getSymbol(), stock);
}
