在Java中增强了for循环和迭代器

Question

I have a class MyList that implements Iterable interface. And here is a toString() method from one of my classes:

public String toString() {
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < 4; i++) {
        // First example using iterator
        for (Iterator<Integer> itr = array[i].iterator(); itr.hasNext();) {
            sb.append(itr.next() + " ");
        }
        // And the same result using enhanced for loop
        for (int val : array[i]) {
            sb.append(val + " ");
        }
    }
    return sb.toString();
}

This loop iterates over the nodes in my list:

for (int val : array[i]) {
    sb.append(val + " ");
}

How does this for loop uses the iterator?

Answer 1

The enhanced for loop works for any class that implements Iterable . It internally calls the iterator() method implemented by that class to obtain an Iterator , and uses hasNext() and next() methods of the Iterator to iterate over the elements of the Iterator .

Answer 2

Because your class ( MyList ) implements Iterable . So internally it will call your iterator() method and then with the use of hasNext() and next() methods of ListIterator it will iterate in for loop.

Refer : Using Enhanced For-Loops with Your Classes