package net.sf.saxon.om;
import net.sf.saxon.expr.LastPositionFinder;
import net.sf.saxon.value.AtomicValue;
import net.sf.saxon.value.SingletonItem;
/**
* SingletonIterator: an iterator over a sequence of zero or one values
*/
public class SingletonIterator implements UnfailingIterator,
net.sf.saxon.expr.ReversibleIterator, LastPositionFinder, GroundedIterator, LookaheadIterator {
private Item item;
private int position = 0;
/**
* Private constructor: external classes should use the factory method
* @param value the item to iterate over
*/
private SingletonIterator(Item value) {
this.item = value;
}
/**
* Factory method.
* @param item the item to iterate over
* @return a SingletonIterator over the supplied item, or an EmptyIterator
* if the supplied item is null.
*/
public static UnfailingIterator makeIterator(Item item) {
if (item==null) {
return EmptyIterator.getInstance();
} else {
return new SingletonIterator(item);
}
}
/**
* Determine whether there are more items to come. Note that this operation
* is stateless and it is not necessary (or usual) to call it before calling
* next(). It is used only when there is an explicit need to tell if we
* are at the last element.
*
* @return true if there are more items
*/
public boolean hasNext() {
return position == 0;
}
public Item next() {
if (position == 0) {
position = 1;
return item;
} else if (position == 1) {
position = -1;
return null;
} else {
return null;
}
}
public Item current() {
if (position == 1) {
return item;
} else {
return null;
}
}
/**
* Return the current position in the sequence.
* @return 0 before the first call on next(); 1 before the second call on next(); -1 after the second
* call on next().
*/
public int position() {
return position;
}
public int getLastPosition() {
return 1;
}
public void close() {
}
public SequenceIterator getAnother() {
return new SingletonIterator(item);
}
public SequenceIterator getReverseIterator() {
return new SingletonIterator(item);
}
public Item getValue() {
return item;
}
/**
* Return a Value containing all the items in the sequence returned by this
* SequenceIterator
*
* @return the corresponding Value. If the value is a closure or a function call package, it will be
* evaluated and expanded.
*/
public GroundedValue materialize() {
if (item instanceof AtomicValue) {
return (AtomicValue)item;
} else {
return new SingletonItem(item);
}
}
/**
* Get properties of this iterator, as a bit-significant integer.
*
* @return the properties of this iterator. This will be some combination of
* properties such as {@link #GROUNDED}, {@link #LAST_POSITION_FINDER},
* and {@link #LOOKAHEAD}. It is always
* acceptable to return the value zero, indicating that there are no known special properties.
* It is acceptable for the properties of the iterator to change depending on its state.
*/
public int getProperties() {
return GROUNDED | LAST_POSITION_FINDER | LOOKAHEAD;
}
}
//
// The contents of this file are subject to the Mozilla Public License Version 1.0 (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.mozilla.org/MPL/
//
// Software distributed under the License is distributed on an "AS IS" basis,
// WITHOUT WARRANTY OF ANY KIND, either express or implied.
// See the License for the specific language governing rights and limitations under the License.
//
// The Original Code is: all this file.
//
// The Initial Developer of the Original Code is Michael H. Kay.
//
// Portions created by (your name) are Copyright (C) (your legal entity). All Rights Reserved.
//
// Contributor(s): none.
//