Class EmptySequence<T extends Item>

java.lang.Object
net.sf.saxon.value.EmptySequence<T>
All Implemented Interfaces:
GroundedValue, Sequence

public final class EmptySequence<T extends Item> extends Object implements GroundedValue
An EmptySequence object represents a sequence containing no members.
  • Field Details

  • Method Details

    • getInstance

      public static <T extends Item> EmptySequence<T> getInstance()
      Get the implicit instance of this class
      Returns:
      the singular instances of this class: an empty sequence
    • getStringValue

      public String getStringValue()
      Description copied from interface: GroundedValue
      Get the string value of this sequence. The string value of an item is the result of applying the 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
      Specified by:
      getStringValue in interface GroundedValue
      Returns:
      the string value of the sequence.
    • getStringValueCS

      public CharSequence getStringValueCS()
      Description copied from interface: GroundedValue
      Get the string value of this sequence. The string value of an item is the result of applying the 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
      Specified by:
      getStringValueCS 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
    • iterate

      public UnfailingIterator iterate()
      Return an iteration over the sequence
      Specified by:
      iterate in interface GroundedValue
      Specified by:
      iterate in interface Sequence
      Returns:
      an iterator (meaning a Saxon SequenceIterator rather than a Java Iterator) over all the items in this Sequence.
    • asItem

      public Item asItem()
      Return the value in the form of an Item
      Returns:
      the value in the form of an Item
    • 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(Object other)
      Is this expression the same as another expression?
      Overrides:
      equals in class Object
      Throws:
      ClassCastException - if the values are not comparable
    • hashCode

      public int hashCode()
      Overrides:
      hashCode in class 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 T 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 String toString()
      Returns a string representation of the object.
      Overrides:
      toString in class 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