| /* |
| * 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.uima.cas.impl; |
| |
| import java.util.ListIterator; |
| import java.util.NoSuchElementException; |
| |
| import org.apache.uima.cas.FSIterator; |
| |
| /** |
| * Class comment for FSListIteratorImpl.java goes here. |
| * |
| * |
| */ |
| class FSListIteratorImpl implements ListIterator { |
| |
| // Keep two pointers: one for the next element, and one for the previous |
| // one. The two pointers are always moved in lockstep. Watch for border |
| // conditions where only one of the pointers is valid. |
| private FSIterator forward; |
| |
| private FSIterator back; |
| |
| public FSListIteratorImpl(FSIterator it) { |
| super(); |
| this.forward = it; |
| this.back = it.copy(); |
| it.moveToPrevious(); |
| } |
| |
| /** |
| * @see ListIterator#hasNext() |
| */ |
| public boolean hasNext() { |
| return this.forward.isValid(); |
| } |
| |
| /** |
| * @see ListIterator#hasPrevious() |
| */ |
| public boolean hasPrevious() { |
| return this.back.isValid(); |
| } |
| |
| /** |
| * Move the iterator so that the next call to {@link #previous() previous()} will return the first |
| * element in the index (for a non-empty index). |
| */ |
| public void moveToEnd() { |
| // Move the back pointer to point at the last element. |
| this.back.moveToLast(); |
| // Move the forward pointer past the end. |
| this.forward.moveToLast(); |
| this.forward.moveToNext(); |
| } |
| |
| /** |
| * Move the iterator so that the next call to {@link #next() next()} will return the first element |
| * in the index (for a non-empty index). |
| */ |
| public void moveToStart() { |
| // Move the forward pointer to the start. |
| this.forward.moveToFirst(); |
| // Move the back pointer past the start. |
| this.back.moveToFirst(); |
| this.back.moveToPrevious(); |
| } |
| |
| /** |
| * @see ListIterator#next() |
| */ |
| public Object next() throws NoSuchElementException { |
| // Throw exception if forward pointer is invalid. |
| if (!this.forward.isValid()) { |
| throw new NoSuchElementException(); |
| } |
| // Move the forward pointer. |
| this.forward.moveToNext(); |
| // Move the backward pointer. Need to check if it's valid. |
| if (this.back.isValid()) { |
| this.back.moveToNext(); |
| } else { |
| // This is guaranteed to yield a valid pointer, since otherwise, the |
| // forward pointer couldn't have been valid. |
| this.back.moveToFirst(); |
| } |
| // The back pointer is now pointing at the current forward element. |
| return this.back.get(); |
| } |
| |
| /** |
| * @see ListIterator#previous() |
| */ |
| public Object previous() throws NoSuchElementException { |
| // See comments for next(). |
| if (!this.back.isValid()) { |
| throw new NoSuchElementException(); |
| } |
| this.back.moveToPrevious(); |
| if (this.forward.isValid()) { |
| this.forward.moveToPrevious(); |
| } else { |
| this.forward.moveToLast(); |
| } |
| return this.forward.get(); |
| } |
| |
| /** |
| * @see java.util.ListIterator#add(Object) |
| */ |
| public void add(Object o) { |
| throw new UnsupportedOperationException(); |
| } |
| |
| /** |
| * @see java.util.ListIterator#nextIndex() |
| */ |
| public int nextIndex() { |
| throw new UnsupportedOperationException(); |
| } |
| |
| /** |
| * @see java.util.ListIterator#previousIndex() |
| */ |
| public int previousIndex() { |
| throw new UnsupportedOperationException(); |
| } |
| |
| /** |
| * @see java.util.Iterator#remove() |
| */ |
| public void remove() { |
| throw new UnsupportedOperationException(); |
| } |
| |
| /** |
| * @see java.util.ListIterator#set(Object) |
| */ |
| public void set(Object o) { |
| throw new UnsupportedOperationException(); |
| } |
| |
| } |