| /* |
| * Copyright (c) 2014 Eike Stepper (Berlin, Germany) and others. |
| * All rights reserved. This program and the accompanying materials |
| * are made available under the terms of the Eclipse Public License v1.0 |
| * which accompanies this distribution, and is available at |
| * http://www.eclipse.org/legal/epl-v10.html |
| * |
| * Contributors: |
| * Eike Stepper - initial API and implementation |
| */ |
| package org.eclipse.oomph.util; |
| |
| import java.util.Iterator; |
| import java.util.ListIterator; |
| import java.util.NoSuchElementException; |
| |
| /** |
| * An abstract base class for custom iterators that only requires to implement a single {@link #computeNextElement()} method. |
| * |
| * @author Eike Stepper |
| */ |
| public abstract class AbstractIterator<T> implements Iterator<T> |
| { |
| /** |
| * The token to be used in {@link #computeNextElement()} to indicate the end of the iteration. |
| */ |
| protected static final Object END_OF_DATA = new Object(); |
| |
| private boolean nextComputed; |
| |
| private T next; |
| |
| public AbstractIterator() |
| { |
| } |
| |
| public final boolean hasNext() |
| { |
| if (nextComputed) |
| { |
| return true; |
| } |
| |
| Object object = computeNextElement(); |
| nextComputed = true; |
| |
| if (object == END_OF_DATA) |
| { |
| return false; |
| } |
| |
| @SuppressWarnings("unchecked") |
| T cast = (T)object; |
| next = cast; |
| return true; |
| } |
| |
| public final T next() |
| { |
| if (!hasNext()) |
| { |
| throw new NoSuchElementException(); |
| } |
| |
| nextComputed = false; |
| return next; |
| } |
| |
| public void remove() |
| { |
| throw new UnsupportedOperationException(); |
| } |
| |
| /** |
| * Returns the next iteration element, or {@link #END_OF_DATA} if the end of the iteration has been reached. |
| */ |
| protected abstract Object computeNextElement(); |
| |
| @SuppressWarnings("unchecked") |
| public static <T> ListIterator<T> empty() |
| { |
| return (ListIterator<T>)EmptyIterator.INSTANCE; |
| } |
| |
| /** |
| * @author Eike Stepper |
| */ |
| private static final class EmptyIterator implements ListIterator<Object> |
| { |
| private static final ListIterator<Object> INSTANCE = new EmptyIterator(); |
| |
| public boolean hasNext() |
| { |
| return false; |
| } |
| |
| public Object next() |
| { |
| throw new NoSuchElementException(); |
| } |
| |
| public boolean hasPrevious() |
| { |
| return false; |
| } |
| |
| public Object previous() |
| { |
| throw new NoSuchElementException(); |
| } |
| |
| public int nextIndex() |
| { |
| throw new NoSuchElementException(); |
| } |
| |
| public int previousIndex() |
| { |
| throw new NoSuchElementException(); |
| } |
| |
| public void remove() |
| { |
| throw new UnsupportedOperationException(); |
| } |
| |
| public void set(Object e) |
| { |
| throw new UnsupportedOperationException(); |
| } |
| |
| public void add(Object e) |
| { |
| throw new UnsupportedOperationException(); |
| } |
| } |
| } |