I had to write my own iterator implementation for my structure which has ArrayList<Vector> field. An iterator is supposed to iterate over mentioned List. Any suggestions on improving it, or anything else?

public class ExamplesIterator implements Iterator<Vector> {

    private List<Vector> examples;  //ArrayList<Vector> will be set here
    private int          index;

    public ExamplesIterator(List<Vector> examples) {
        this.examples = examples;
        index = 0;

    public Vector next() {
        if(hasNext()) {
            return examples.get(index++);
        } else {
            throw new NoSuchElementException("There are no elements size = " + examples.size());

    public boolean hasNext() {
        return !(examples.size() == index);

    public void remove() {
        if(index <= 0) {
            throw new IllegalStateException("You can't delete element before first next() method call");

1 Answer 1


I think your implementation is overall very good, two small comments:

  • Improving readability for return statement in hasNext to return examples.size() != index;
  • Making the examples field final: private final List<Vector> examples;

However, if the Vector class here is java.util.Vector you should know that it is considered deprecated in favor of the ArrayList class.

Also, since you create your iterator from a List<Vector> you could get an Iterator<Vector> by calling list.iterator();

  • \$\begingroup\$ Well... I completely forgot about that I can call list.iterator(); :P. Thank you ! \$\endgroup\$
    – ashur
    Commented Nov 19, 2013 at 20:13

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