CODEWITHSUNDEEP
javaforeachiterator
jaynp
jaynp

Reputation: 3325

Using for-each loop with a function that returns an iterator

How can I use a for each loop with a function that returns an iterator in Java? For example, I'd like to use a for-each loop for a function with this signature:

public Iterator<Integer> intIterator();

Is it possible or do I have to use a regular for-loop?

Upvotes: 0

Views: 218

Answers (3)

user2357112
user2357112

Reputation: 280227

Unfortunately, Java's for-each is defined to require an Iterable, and Iterators aren't Iterable. This can be a pain if, say, you want to provide 3 kinds of iterator for a tree or forward and backward iterators over a data structure.

The easiest way is to use a regular for loop, but if you want, you can write a wrapper class, like so:

public class IteratorWrapper<E> implements Iterable<E> {
    private Iterator<E> iterator;

    public IteratorWrapper(Iterator<E> iterator) {
        this.iterator = iterator;
    }

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

    // Static import the following method for less typing at the
    // call sites.
    public static <E> IteratorWrapper<E> wrapIter(Iterator<E> iterator) {
        return new IteratorWrapper<E>(iterator);
    }
}

Upvotes: 4

Chip
Chip

Reputation: 3316

You cannot directly use the iterator as other people have said.

Make another function : 

public Iterable<Integer> intIterable() {
    return new Iterable<Integer>() {
        @Override
        public Iterator<Integer> iterator() {
                    return intIterator();
        }
    }
}

Use in for-each loop like 

for ( Integer int : object.intIterable() ) {
}

Upvotes: 0

Subhrajyoti Majumder
Subhrajyoti Majumder

Reputation: 41200

for-each loop can only iterate over an array or an instance of java.lang.Iterable. you can not do it.

you can iterate like - 

Iterator<Integer> iterator = intIterator();
for (; iterator.hasNext();) {
    Integer type =  iterator.next();
}

Upvotes: 0

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