ArrayListIterator.java
/*
* 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.lang.reflect.Array;
import java.util.NoSuchElementException;
import org.apache.commons.collections4.ResettableListIterator;
/**
* Implements a {@link java.util.ListIterator} over an array.
* <p>
* The array can be either an array of object or of primitives. If you know
* that you have an object array, the {@link ObjectArrayListIterator}
* class is a better choice, as it will perform better.
*
* <p>
* This iterator does not support {@link #add(Object)} or {@link #remove()}, as the array
* cannot be changed in size. The {@link #set(Object)} method is supported however.
*
* @param <E> the type of elements returned by this iterator.
* @see org.apache.commons.collections4.iterators.ArrayIterator
* @see java.util.Iterator
* @see java.util.ListIterator
*
* @since 3.0
*/
public class ArrayListIterator<E> extends ArrayIterator<E>
implements ResettableListIterator<E> {
/**
* Holds the index of the last item returned by a call to {@code next()}
* or {@code previous()}. This is set to {@code -1} if neither method
* has yet been invoked. {@code lastItemIndex} is used to implement
* the {@link #set} method.
*/
private int lastItemIndex = -1;
/**
* Constructs an ArrayListIterator that will iterate over the values in the
* specified array.
*
* @param array the array to iterate over
* @throws IllegalArgumentException if {@code array} is not an array.
* @throws NullPointerException if {@code array} is {@code null}
*/
public ArrayListIterator(final Object array) {
super(array);
}
/**
* Constructs an ArrayListIterator that will iterate over the values in the
* specified array from a specific start index.
*
* @param array the array to iterate over
* @param startIndex the index to start iterating at
* @throws IllegalArgumentException if {@code array} is not an array.
* @throws NullPointerException if {@code array} is {@code null}
* @throws IndexOutOfBoundsException if the start index is out of bounds
*/
public ArrayListIterator(final Object array, final int startIndex) {
super(array, startIndex);
}
/**
* Constructs an ArrayListIterator that will iterate over a range of values
* in the specified array.
*
* @param array the array to iterate over
* @param startIndex the index to start iterating at
* @param endIndex the index (exclusive) to finish iterating at
* @throws IllegalArgumentException if {@code array} is not an array.
* @throws IndexOutOfBoundsException if the start or end index is out of bounds
* @throws IllegalArgumentException if end index is before the start
* @throws NullPointerException if {@code array} is {@code null}
*/
public ArrayListIterator(final Object array, final int startIndex, final int endIndex) {
super(array, startIndex, endIndex);
}
/**
* This iterator does not support modification of its backing collection, and so will
* always throw an {@link UnsupportedOperationException} when this method is invoked.
*
* @param o the element to add
* @throws UnsupportedOperationException always thrown.
* @see java.util.ListIterator#set
*/
@Override
public void add(final Object o) {
throw new UnsupportedOperationException("add() method is not supported");
}
// ListIterator interface
/**
* Returns true if there are previous elements to return from the array.
*
* @return true if there is a previous element to return
*/
@Override
public boolean hasPrevious() {
return this.index > this.startIndex;
}
/**
* Gets the next element from the array.
*
* @return the next element
* @throws NoSuchElementException if there is no next element
*/
@Override
@SuppressWarnings("unchecked")
public E next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
this.lastItemIndex = this.index;
return (E) Array.get(this.array, this.index++);
}
/**
* Gets the next index to be retrieved.
*
* @return the index of the item to be retrieved next
*/
@Override
public int nextIndex() {
return this.index - this.startIndex;
}
/**
* Gets the previous element from the array.
*
* @return the previous element
* @throws NoSuchElementException if there is no previous element
*/
@Override
@SuppressWarnings("unchecked")
public E previous() {
if (!hasPrevious()) {
throw new NoSuchElementException();
}
this.lastItemIndex = --this.index;
return (E) Array.get(this.array, this.index);
}
/**
* Gets the index of the item to be retrieved if {@link #previous()} is called.
*
* @return the index of the item to be retrieved next
*/
@Override
public int previousIndex() {
return this.index - this.startIndex - 1;
}
/**
* Resets the iterator back to the start index.
*/
@Override
public void reset() {
super.reset();
this.lastItemIndex = -1;
}
/**
* Sets the element under the cursor.
* <p>
* This method sets the element that was returned by the last call
* to {@link #next()} of {@link #previous()}.
* <p>
* <b>Note:</b> {@link java.util.ListIterator} implementations that support
* {@code add()} and {@code remove()} only allow {@code set()} to be called
* once per call to {@code next()} or {@code previous} (see the {@link java.util.ListIterator}
* Javadoc for more details). Since this implementation does
* not support {@code add()} or {@code remove()}, {@code set()} may be
* called as often as desired.
*
* @param o the element to set
* @throws IllegalStateException if {@link #next()} or {@link #previous()} has not been called
* before {@link #set(Object)}
* @see java.util.ListIterator#set
*/
@Override
public void set(final Object o) {
if (this.lastItemIndex == -1) {
throw new IllegalStateException("must call next() or previous() before a call to set()");
}
Array.set(this.array, this.lastItemIndex, o);
}
}