/* | |
* 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; | |
import org.apache.uima.cas.FeatureStructure; | |
/** | |
* Class comment for FSListIteratorImpl.java goes here. | |
* | |
* | |
*/ | |
class FSListIteratorImpl<T extends FeatureStructure> implements ListIterator<T> { | |
// 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<T> forward; | |
private FSIterator<T> back; | |
public FSListIteratorImpl(FSIterator<T> 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 T 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 T 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(T 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(T) | |
*/ | |
public void set(T o) { | |
throw new UnsupportedOperationException(); | |
} | |
} |