Class EmptySequence

    • Method Detail

      • getInstance

        public static EmptySequence getInstance()
        Get the implicit instance of this class
      • iterate

        public SequenceIterator iterate()
        Return an iteration over the sequence
        Specified by:
        iterate in class Value
        Returns:
        an iterator over the sequence of items
      • asItem

        public Item asItem()
        Return the value in the form of an Item
        Overrides:
        asItem in class Value
        Returns:
        the value in the form of an Item
      • getItemType

        public ItemType getItemType​(TypeHierarchy th)
        Determine the item type
        Overrides:
        getItemType in class Value
        Parameters:
        th - the type hierarchy cache
        Returns:
        for the default implementation: AnyItemType (not known)
      • getCardinality

        public int getCardinality()
        Determine the static cardinality
        Overrides:
        getCardinality in class Value
        Returns:
        the cardinality
      • getLength

        public final int getLength()
        Get the length of the sequence
        Overrides:
        getLength in class Value
        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 Value
        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
        Overrides:
        effectiveBooleanValue in class Value
        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
        Overrides:
        itemAt in class Value
        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