迭代器实现导致无限循环

Question

I am trying to do a foreach loop as followed for a linkedlist-esque class I built:

boolean contains = false;
for(Thing t : front) {
    if(t.equals(something)) {
        t.doSomething();
        contains = true;
        break;
    } 
}

This are the iterator methods I've implemented:

@Override
public Iterator<Thing> iterator() {
    Thing current = this;
    return new Iterator<Thing>() {
        public boolean hasNext() {
            return current.hasNext();
        }

        public Thing next() {
            return current.next;
        }
    };
}

I've tried debugging this and it seems it isn't returning the next element in the linkedlist, thus causing an infinite loop when I run it and try and do a foreach loop.

Sorry if this question has been answered or there's a really stupid mistake, I searched for a while and couldn't find an answer. This is my first time writing an iterator so please be gentle. :)

Answer 1

You have to advance the Iterator 's state in next() :

    public Thing next() {
        current = current.next;
        return current;
    }

Otherwise, all calls to next() would return the same element.

EDIT :

You should move your local variable declaration Thing current = this; inside your anonymous class instance (ie turn it into an instance variable).

@Override
public Iterator<Thing> iterator() {
    return new Iterator<Thing>() {

        private Thing current = Thing.this;

        public boolean hasNext() {
            return current.hasNext();
        }

        public Thing next() {
            current = current.next;
            return current;
        }

    };
}