Package net.sf.saxon.om

Class ZeroOrOne<T extends Item>

  • All Implemented Interfaces:
    GroundedValue, Sequence
    Direct Known Subclasses:
    One
    public class ZeroOrOne<T extends Item>
extends java.lang.Object
implements GroundedValue
    A value that is a sequence containing zero or one items.

    • Constructor Detail

      • ZeroOrOne

        public ZeroOrOne​(T item)
        Create a sequence containing zero or one items
        Parameters:
        item - The item to be contained in the sequence, or null if the sequence is to be empty

    • Method Detail

      • empty

        public static <T extends Item> ZeroOrOne<T> empty()
        Return the instance of ZeroOrOne that represents the empty sequence
        Type Parameters:
        T - the static type of the empty sequence
        Returns:
        a representation of the empty sequence that satisfies the type ZeroOrOne

      • getUnicodeStringValue

        public UnicodeString getUnicodeStringValue()
        Convert the value to a string, using the serialization rules. For atomic values this is the same as a cast; for sequence values it gives a space-separated list. For QNames and NOTATIONS, or lists containing them, it fails.
        Specified by:
        getUnicodeStringValue in interface GroundedValue
        Returns:
        the string value

      • getStringValue

        public java.lang.String getStringValue()
        Description copied from interface: GroundedValue
        Get the string value of this sequence, as an instance of String. The string value of an item is the result of applying the XPath string() function. The string value of a sequence is the space-separated result of applying the string-join() function using a single space as the separator.

        The result of this method is always equivalent to the result of the GroundedValue.getUnicodeStringValue() method. Use this method in preference either (a) if you need to use the value in a context where a String is required, or (b) if the underlying value is held as a String, or in a form that is readily converted to a String. This is typically the case (i) when the value is an attribute node in a TinyTree, or (ii) any kind of node in a third-party tree model such as DOM.

        Specified by:
        getStringValue in interface GroundedValue
        Returns:
        the string value of the sequence.

      • head

        public T head()
        Get the first item in the sequence.
        Specified by:
        head in interface GroundedValue
        Specified by:
        head in interface Sequence
        Returns:
        the first item in the sequence if there is one, or null if the sequence is empty

      • getLength

        public int getLength()
        Get the length of the sequence
        Specified by:
        getLength in interface GroundedValue
        Returns:
        the number of items in the sequence. Note that for a single item, including a map or array, the result is always 1 (one).

      • itemAt

        public T itemAt​(int n)
        Get the n'th item in the sequence (starting from 0). This is defined for all SequenceValues, but its real benefits come for a SequenceValue stored extensionally (or for a MemoClosure, once all the values have been read)
        Specified by:
        itemAt in interface GroundedValue
        Parameters:
        n - the index of the required item, with 0 representing the first item in the sequence
        Returns:
        the n'th item if it exists, or null otherwise

      • subsequence

        public GroundedValue subsequence​(int start,
                                 int length)
        Get a subsequence of the value
        Specified by:
        subsequence in interface GroundedValue
        Parameters:
        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
        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
        Returns:
        the required subsequence. If min is

      • effectiveBooleanValue

        public boolean effectiveBooleanValue()
                              throws XPathException
        Get the effective boolean value
        Specified by:
        effectiveBooleanValue in interface GroundedValue
        Returns:
        the effective boolean value
        Throws:
        XPathException - if the sequence has no effective boolean value (for example a sequence of two integers)

      • toString

        public java.lang.String toString()
        Returns a string representation of the object (used only for diagnostics).
        Overrides:
        toString in class java.lang.Object
        Returns:
        a string representation of the object.

      • reduce

        public GroundedValue reduce()
        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.
        Specified by:
        reduce in interface GroundedValue
        Returns:
        the simplified sequence