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An OSGi bundle for Saxon-HE
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2013 Saxonica Limited.
// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
// If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
// This Source Code Form is "Incompatible With Secondary Licenses", as defined by the Mozilla Public License, v. 2.0.
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
package net.sf.saxon.value;
import net.sf.saxon.expr.StaticProperty;
import net.sf.saxon.om.GroundedValue;
import net.sf.saxon.om.Item;
import net.sf.saxon.om.SequenceIterator;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.tree.iter.EmptyIterator;
import net.sf.saxon.type.ErrorType;
import net.sf.saxon.type.ItemType;
import net.sf.saxon.type.TypeHierarchy;
/**
* An EmptySequence object represents a sequence containing no members.
*/
public final class EmptySequence implements GroundedValue {
// This class has a single instance
/*@NotNull*/ private static EmptySequence THE_INSTANCE = new EmptySequence();
/**
* Private constructor: only the predefined instances of this class can be used
*/
private EmptySequence() {}
/**
* Get the implicit instance of this class
* @return the singular instances of this class: an empty sequence
*/
/*@NotNull*/ public static EmptySequence getInstance() {
return THE_INSTANCE;
}
public String getStringValue() throws XPathException {
return "";
}
public CharSequence getStringValueCS() throws XPathException {
return "";
}
/**
* Get the first item in the sequence.
*
* @return the first item in the sequence if there is one, or null if the sequence
* is empty
* @throws net.sf.saxon.trans.XPathException
* in the situation where the sequence is evaluated lazily, and
* evaluation of the first item causes a dynamic error.
*/
public Item head() throws XPathException {
return null;
}
/**
* Return an iteration over the sequence
*/
/*@NotNull*/ public SequenceIterator iterate() {
return EmptyIterator.emptyIterator();
}
/**
* Return the value in the form of an Item
* @return the value in the form of an Item
*/
/*@Nullable*/ public Item asItem() {
return null;
}
/**
* Determine the item type
* @param th the type hierarchy cache
*/
/*@NotNull*/
public ItemType getItemType(/*@NotNull*/ TypeHierarchy th) {
return ErrorType.getInstance();
}
/**
* Determine the static cardinality
*/
public int getCardinality() {
return StaticProperty.EMPTY;
}
/**
* Get the length of the sequence
* @return always 0 for an empty sequence
*/
public final int getLength() {
return 0;
}
/**
* Is this expression the same as another expression?
* @throws ClassCastException if the values are not comparable
*/
public boolean equals(/*@NotNull*/ Object other) {
if (!(other instanceof EmptySequence)) {
throw new ClassCastException("Cannot compare " + other.getClass() + " to empty sequence");
}
return true;
}
public int hashCode() {
return 42;
}
/**
* Get the effective boolean value - always false
*/
public boolean effectiveBooleanValue() {
return false;
}
/**
* Get the n'th item in the sequence (starting from 0). This is defined for all
* Values, but its real benefits come for a sequence Value stored extensionally
* (or for a MemoClosure, once all the values have been read)
*
* @param n position of the required item, counting from zero.
* @return the n'th item in the sequence, where the first item in the sequence is
* numbered zero. If n is negative or >= the length of the sequence, returns null.
*/
/*@Nullable*/ public T itemAt(int n) {
return null;
}
/**
* Get a subsequence of the value
*
*
* @param min the index of the first item to be included in the result, counting from zero.
* A negative value is taken as zero. If the value is beyond the end of the sequence, an empty
* sequence is returned
* @param length the number of items to be included in the result. Specify Integer.MAX_VALUE to
* get the subsequence up to the end of the base sequence. If the value is negative, an empty sequence
* is returned. If the value goes off the end of the sequence, the result returns items up to the end
* of the sequence
* @return the required subsequence. If min is
*/
/*@NotNull*/ public GroundedValue subsequence(int min, int length) {
return this;
}
/**
* Returns a string representation of the object.
*/
/*@NotNull*/ public String toString() {
return "()";
}
/**
* Reduce the sequence to its simplest form. If the value is an empty sequence, the result will be
* EmptySequence.getInstance(). If the value is a single atomic value, the result will be an instance
* of AtomicValue. If the value is a single item of any other kind, the result will be an instance
* of SingletonItem. Otherwise, the result will typically be unchanged.
*
* @return the simplified sequence
*/
public GroundedValue reduce() {
return this;
}
}