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The XSLT and XQuery Processor
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2018-2022 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.om;
import net.sf.saxon.str.UnicodeString;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.tree.iter.SingletonIterator;
import net.sf.saxon.value.EmptySequence;
/**
* An Item is an object that can occur as a member of a sequence.
* It corresponds directly to the concept of an item in the XPath 2.0 data model.
* There are four kinds of Item: atomic values, nodes, function items, and external objects.
* This interface is part of the public Saxon API. As such (starting from Saxon 8.4),
* methods that form part of the stable API are labelled with a JavaDoc "since" tag
* to identify the Saxon release at which they were introduced.
* Note: there is no method getItemType(). This is to avoid having to implement it
* on every implementation of NodeInfo. Instead, use the static method Type.getItemType(Item).
*
*/
public interface Item extends GroundedValue {
/**
* Get the genre of this item (to distinguish the top-level categories of item,
* such as nodes, atomic values, and functions)
* @return the genre
*/
Genre getGenre();
/**
* Get the first item in the sequence. Differs from the superclass {@link Sequence} in that
* * no exception is thrown.
*
* @return the first item in the sequence if there is one, or null if the sequence
* is empty
*/
@Override
default Item head() {
return this;
}
/**
* Get the value of the item as a Unicode string. For nodes, this is the string value of the
* node as defined in the XPath 2.0 data model, except that all nodes are treated as being
* untyped: it is not an error to get the string value of a node with a complex type.
* For atomic values, the method returns the result of casting the atomic value to a string.
*
* @return the string value of the item
* @throws UnsupportedOperationException if the item is a function item (an unchecked exception
* is used here to avoid introducing exception handling to a large number of paths where it is not
* needed)
* @since 8.4
*/
@Override
UnicodeString getUnicodeStringValue();
/**
* Get the value of the item as a Java string. For nodes, this is the string value of the
* node as defined in the XPath 2.0 data model, except that all nodes are treated as being
* untyped: it is not an error to get the string value of a node with a complex type.
* For atomic values, the method returns the result of casting the atomic value to a string.
*
* @return the string value of the item
* @throws UnsupportedOperationException if the item is a function item (an unchecked exception
* is used here to avoid introducing exception handling to a large number of paths where it is not
* needed)
* @since 8.4
*/
@Override
default String getStringValue() {
return getUnicodeStringValue().toString();
}
/**
* Atomize the item.
* @return the result of atomization
* @throws net.sf.saxon.trans.XPathException if atomization is not allowed
* for this kind of item
*/
AtomicSequence atomize() throws XPathException;
/**
* Provide a short string showing the contents of the item, suitable
* for use in error messages
* @return a depiction of the item suitable for use in error messages
*/
@Override
default String toShortString() {
return toString();
}
/**
* Get the n'th item in the value, counting from 0
*
* @param n the index of the required item, with 0 representing the first item in the sequence
* @return the n'th item if it exists, or null otherwise
*/
@Override
default Item itemAt(int n) {
return n == 0 ? head() : null;
}
/**
* Get a subsequence of the value
*
* @param start 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
*/
@Override
default GroundedValue subsequence(int start, int length) {
if (start <= 0 && (start + length) > 0) {
return this;
} else {
return EmptySequence.getInstance();
}
}
/**
* Get the size of the value (the number of items)
*
* @return the number of items in the sequence. Note that for a single item, including a map or array,
* the result is always 1 (one).
*/
@Override
default int getLength() {
return 1;
}
/**
* Get an iterator over all the items in the sequence
*
* @return an iterator over all the items
*/
@Override
default SingletonIterator iterate() {
return new SingletonIterator(this);
}
/**
* 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 Item. Otherwise, the result will typically be unchanged.
*
* @return the simplified sequence
*/
@Override
default GroundedValue reduce() {
return this;
}
/**
* Ask whether this is a node in a streamed document
*
* @return true if the node is in a document being processed using streaming
*/
default boolean isStreamed() {
return false;
}
}