com.github.javaparser.printer.lexicalpreservation.PeekingIterator Maven / Gradle / Ivy
Show all versions of stubparser Show documentation
/*
* Copyright (C) 2011, 2013-2024 The JavaParser Team.
*
* This file is part of JavaParser.
*
* JavaParser can be used either under the terms of
* a) the GNU Lesser General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
* b) the terms of the Apache License
*
* You should have received a copy of both licenses in LICENCE.LGPL and
* LICENCE.APACHE. Please refer to those files for details.
*
* JavaParser is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*/
package com.github.javaparser.printer.lexicalpreservation;
import java.util.List;
import java.util.ListIterator;
import java.util.NoSuchElementException;
import java.util.Objects;
/**
* Decorates an iterator to support one-element lookahead while iterating.
*
* The decorator supports the removal operation, but an {@link IllegalStateException}
* will be thrown if {@link #remove()}, {@link #add()}, {@link #set()}} is called directly after a call to
* {@link #peek()} or {@link #element()}.
*
* @param the type of elements returned by this iterator.
* @since 4.0
*/
public class PeekingIterator implements ListIterator, LookaheadIterator {
/**
* The iterator being decorated.
*/
private final ListIterator iterator;
/**
* Indicates that the decorated iterator is exhausted.
*/
private boolean exhausted;
/**
* Indicates if the lookahead slot is filled.
*/
private boolean slotFilled;
/**
* The current slot for lookahead.
*/
private E slot;
/**
* Decorates the specified iterator to support one-element lookahead.
*
* If the iterator is already a {@link PeekingIterator} it is returned directly.
*
* @param the element type
* @param iterator the iterator to decorate
* @return a new peeking iterator
* @throws NullPointerException if the iterator is null
*/
public PeekingIterator peekingIterator(final ListIterator iterator) {
Objects.requireNonNull(iterator, "iterator");
if (iterator instanceof PeekingIterator) {
final PeekingIterator it = (PeekingIterator) iterator;
return it;
}
return new PeekingIterator<>(iterator);
}
/**
* Constructor.
*
* @param iterator the iterator to decorate
*/
public PeekingIterator(final ListIterator iterator) {
this.iterator = iterator;
}
/**
* Constructor.
*
* @param list the provider of the iterator to decorate
*/
public PeekingIterator(final List list) {
this.iterator = list.listIterator();
}
private void fill() {
if (exhausted || slotFilled) {
return;
}
if (iterator.hasNext()) {
slot = iterator.next();
slotFilled = true;
} else {
exhausted = true;
slot = null;
slotFilled = false;
}
}
@Override
public boolean hasNext() {
if (exhausted) {
return false;
}
return slotFilled || iterator.hasNext();
}
/**
* Returns the next element in iteration without advancing the underlying iterator.
* If the iterator is already exhausted, null will be returned.
*
* Note: this method does not throw a {@link NoSuchElementException} if the iterator
* is already exhausted. If you want such a behavior, use {@link #element()} instead.
*
* The rationale behind this is to follow the {@link java.util.Queue} interface
* which uses the same terminology.
*
* @return the next element from the iterator
*/
@Override
public E peek() {
fill();
return exhausted ? null : slot;
}
/**
* Returns the next element in iteration without advancing the underlying iterator.
* If the iterator is already exhausted, null will be returned.
*
* @return the next element from the iterator
* @throws NoSuchElementException if the iterator is already exhausted according to {@link #hasNext()}
*/
@Override
public E element() {
fill();
if (exhausted) {
throw new NoSuchElementException();
}
return slot;
}
@Override
public E next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
final E x = slotFilled ? slot : iterator.next();
// reset the lookahead slot
slot = null;
slotFilled = false;
return x;
}
/**
* {@inheritDoc}
*
* @throws IllegalStateException if {@link #peek()} or {@link #element()} has been called
* prior to the call to {@link #remove()}
*/
@Override
public void remove() {
if (slotFilled) {
throw new IllegalStateException("peek() or element() called before remove()");
}
iterator.remove();
}
@Override
public boolean hasPrevious() {
return iterator.hasPrevious();
}
@Override
public E previous() {
return iterator.previous();
}
@Override
public int nextIndex() {
return iterator.nextIndex();
}
/*
* Returns the index of the element that would be returned by the last call to next.
* Returns list size - 1 if the listiterator is at the end of the list.
* Returns -1 if the listiterator is at the beginning of the list.
*/
public int currentIndex() {
if (!hasPrevious()) return previousIndex();
return nextIndex() - 1;
}
@Override
public int previousIndex() {
return iterator.previousIndex();
}
@Override
public void set(E e) {
if (slotFilled) {
throw new IllegalStateException("peek() or element() called before set()");
}
iterator.set(e);
}
@Override
public void add(E e) {
if (slotFilled) {
throw new IllegalStateException("peek() or element() called before add()");
}
iterator.add(e);
}
}