Package net.sf.saxon.om

Class ZeroOrOne<T extends Item<?>>

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

  • Constructor Details

    • 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 Details

    • empty

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

    • getStringValueCS

      public CharSequence getStringValueCS()
      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 an empty sequence is the zero-length string.
      Specified by:
      getStringValueCS in interface GroundedValue<T extends Item<?>>
      Returns:
      the string value of the sequence.

    • getStringValue

      public String getStringValue()
      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:
      getStringValue in interface GroundedValue<T extends Item<?>>
      Returns:
      the string value of the sequence.

    • head

      public T head()
      Get the first item in the sequence.
      Specified by:
      head in interface GroundedValue<T extends Item<?>>
      Specified by:
      head in interface Sequence<T extends Item<?>>
      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<T extends Item<?>>
      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<T extends Item<?>>
      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<T> subsequence(int start, int length)
      Get a subsequence of the value
      Specified by:
      subsequence in interface GroundedValue<T extends Item<?>>
      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

    • iterate

      public UnfailingIterator<T> iterate()
      Return an enumeration of this nodeset value.
      Specified by:
      iterate in interface GroundedValue<T extends Item<?>>
      Specified by:
      iterate in interface Sequence<T extends Item<?>>
      Returns:
      an iterator (meaning a Saxon SequenceIterator rather than a Java Iterator) over all the items in this Sequence.

    • effectiveBooleanValue

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

    • toString

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

    • reduce

      public GroundedValue<T> 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<T extends Item<?>>
      Returns:
      the simplified sequence