For-eaching an iterator

[Stuart Ash]

The J5 for-each takes an iterable, and collections have been retrofitted to be iterable, thus avoiding the programmer having to extract an iterator.

Now, what if some API gives me only an iterator, is there a way someone can use the for-each loop for its brevity over such an iterator. Any workarounds?

[Jesper de Jong]

If you only have an Iterator (not an Iterable), I don't think there's a way to use it with the "for each" loop.

If you really want to do it, you could write a simple class that implements interface Iterable (not tested and not sure about the generics):

public class MyIteratorWrapper<T> implements Iterable<T> {
    private Iterator<T> iter;
 
    public MyIteratorWrapper(Iterator<T> iter) {
        this.iter = iter;
    }
 
    public Iterator<T> iterator() {
        return iter;
    }
}
 
// use it
MyIteratorWrapper w = new MyIteratorWrapper(iter);
 
for (Object o : w) {
    // ...do something
}

[Stuart Ash]

Hi Jesper,

I tried out your code, with refinements. It works! I'll add this to my personal lib, thanks

 
 
public class IterableTest {
 
public static void main(String[] args) {
List<String> list = new ArrayList<String>();
list.add("a");list.add("b");list.add("c");
 
// do it as though you can't get the collection 
Iterator<String> iterator = list.iterator();

for(String str : new IteratorIterable<String>(iterator)) {
System.out.println(str);
}
}
 
}
 
public class IteratorIterable<T> implements Iterable<T>
{
private Iterator<T> iterator;

public IteratorIterable(Iterator<T> iterator) {
this.iterator = iterator;
}

public Iterator<T> iterator() {
return iterator;
}
}

[Ilja Preuss]

By the way, this is the Adapter design pattern in action...

[Stuart Ash]

Originally posted by Ilja Preuss:
By the way, this is the Adapter design pattern in action...

Yeah, that's why I named it that way - even though different from Jesper's suggestion.