Package net.sf.saxon.value

Class EmptySequence

  • All Implemented Interfaces:
    GroundedValue, Sequence
    public final class EmptySequence
extends java.lang.Object
implements GroundedValue
    An EmptySequence object represents a sequence containing no members.
    Since:
    9.5. Generified in 9.9. Generification reverted in 11.0.

    • Method Detail

      • getInstance

        public static EmptySequence getInstance()
        Get the implicit instance of this class
        Returns:
        the singular instances of this class: an empty sequence

      • getUnicodeStringValue

        public UnicodeString getUnicodeStringValue()
        Description copied from interface: GroundedValue
        Get the string value of this sequence, as an instance of UnicodeString. 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.getStringValue() method. Use this method in preference either (a) if you need to use the value in a context where a UnicodeString is required, or (b) if the underlying value is held as a UnicodeString, or in a form that is readily converted to a UnicodeString. This is typically the case (i) when the value is a text or element node in a TinyTree, and (ii) when the value is a StringItem: that is, an atomic value of type xs:string.

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

      • 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 Item 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 final int getLength()
        Get the length of the sequence
        Specified by:
        getLength in interface GroundedValue
        Returns:
        always 0 for an empty sequence

      • equals

        public boolean equals​(java.lang.Object other)
        Is this expression the same as another expression?
        Overrides:
        equals in class java.lang.Object
        Throws:
        java.lang.ClassCastException - if the values are not comparable

      • hashCode

        public int hashCode()
        Overrides:
        hashCode in class java.lang.Object

      • effectiveBooleanValue

        public boolean effectiveBooleanValue()
        Get the effective boolean value - always false
        Specified by:
        effectiveBooleanValue in interface GroundedValue
        Returns:
        the effective boolean value

      • itemAt

        public Item itemAt​(int n)
        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)
        Specified by:
        itemAt in interface GroundedValue
        Parameters:
        n - position of the required item, counting from zero.
        Returns:
        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.

      • subsequence

        public GroundedValue subsequence​(int min,
                                 int length)
        Get a subsequence of the value
        Specified by:
        subsequence in interface GroundedValue
        Parameters:
        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
        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

      • toString

        public java.lang.String toString()
        Returns a string representation of the object.
        Overrides:
        toString in class java.lang.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