/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.collections4.iterators;

import java.util.Collection;
import java.util.Iterator;
import java.util.NoSuchElementException;

import org.apache.commons.collections4.ResettableIterator;

An Iterator that restarts when it reaches the end.
 The iterator will loop continuously around the provided elements, unless there are no elements in the collection to begin with, or all the elements have been removed. 

Concurrent modifications are not directly supported, and for most collection
implementations will throw a ConcurrentModificationException.
Since:
3.0/**
 * An Iterator that restarts when it reaches the end.
 * <p>
 * The iterator will loop continuously around the provided elements, unless
 * there are no elements in the collection to begin with, or all the elements
 * have been {@link #remove removed}.
 * <p>
 * Concurrent modifications are not directly supported, and for most collection
 * implementations will throw a ConcurrentModificationException.
 *
 * @since 3.0
 */
public class LoopingIterator<E> implements ResettableIterator<E> {

    
The collection to base the iterator on /** The collection to base the iterator on */
    private final Collection<? extends E> collection;
    
The current iterator /** The current iterator */
    private Iterator<? extends E> iterator;

    
Constructor that wraps a collection.

There is no way to reset an Iterator instance without recreating it from
the original source, so the Collection must be passed in.
Params:
coll –  the collection to wrap
Throws:
NullPointerException – if the collection is null/**
     * Constructor that wraps a collection.
     * <p>
     * There is no way to reset an Iterator instance without recreating it from
     * the original source, so the Collection must be passed in.
     *
     * @param coll  the collection to wrap
     * @throws NullPointerException if the collection is null
     */
    public LoopingIterator(final Collection<? extends E> coll) {
        if (coll == null) {
            throw new NullPointerException("The collection must not be null");
        }
        collection = coll;
        reset();
    }

    
Has the iterator any more elements.
 Returns false only if the collection originally had zero elements, or all the elements have been removed. 
Returns:
true if there are more elements/**
     * Has the iterator any more elements.
     * <p>
     * Returns false only if the collection originally had zero elements, or
     * all the elements have been {@link #remove removed}.
     *
     * @return <code>true</code> if there are more elements
     */
    @Override
    public boolean hasNext() {
        return collection.size() > 0;
    }

    
Returns the next object in the collection.

If at the end of the collection, return the first element.
Throws:
NoSuchElementException – if there are no elements at all. Use hasNext to avoid this error.
Returns:
the next object/**
     * Returns the next object in the collection.
     * <p>
     * If at the end of the collection, return the first element.
     *
     * @return the next object
     * @throws NoSuchElementException if there are no elements
     *         at all.  Use {@link #hasNext} to avoid this error.
     */
    @Override
    public E next() {
        if (collection.size() == 0) {
            throw new NoSuchElementException("There are no elements for this iterator to loop on");
        }
        if (iterator.hasNext() == false) {
            reset();
        }
        return iterator.next();
    }

    
Removes the previously retrieved item from the underlying collection.
 This feature is only supported if the underlying collection's iterator method returns an implementation that supports it. 
 This method can only be called after at least one next method call. After a removal, the remove method may not be called again until another next has been performed. If the reset is called, then remove may not be called until next is called again. /**
     * Removes the previously retrieved item from the underlying collection.
     * <p>
     * This feature is only supported if the underlying collection's
     * {@link Collection#iterator iterator} method returns an implementation
     * that supports it.
     * <p>
     * This method can only be called after at least one {@link #next} method call.
     * After a removal, the remove method may not be called again until another
     * next has been performed. If the {@link #reset} is called, then remove may
     * not be called until {@link #next} is called again.
     */
    @Override
    public void remove() {
        iterator.remove();
    }

    
Resets the iterator back to the start of the collection.
/**
     * Resets the iterator back to the start of the collection.
     */
    @Override
    public void reset() {
        iterator = collection.iterator();
    }

    
Gets the size of the collection underlying the iterator.
Returns:
the current collection size/**
     * Gets the size of the collection underlying the iterator.
     *
     * @return the current collection size
     */
    public int size() {
        return collection.size();
    }

}