ZeroOrOne

java.lang.Object
- net.sf.saxon.om.ZeroOrOne<T>

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 Summary

Constructors
Constructor and Description

ZeroOrOne(T item)
Create a sequence containing zero or one items

Constructors
Constructor and Description
`ZeroOrOne(T item)` Create a sequence containing zero or one items

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`boolean`	`effectiveBooleanValue()` Get the effective boolean value
`static <T extends Item> ZeroOrOne<T>`	`empty()` Return the instance of ZeroOrOne that represents the empty sequence
`int`	`getLength()` Get the length of the sequence
`java.lang.String`	`getStringValue()` Get the string value of this sequence, as an instance of `String`.
`UnicodeString`	`getUnicodeStringValue()` Convert the value to a string, using the serialization rules.
`T`	`head()` Get the first item in the sequence.
`T`	`itemAt(int n)` Get the n'th item in the sequence (starting from 0).
`SequenceIterator`	`iterate()` Return an iterator over this value.
`GroundedValue`	`reduce()` Reduce the sequence to its simplest form.
`GroundedValue`	`subsequence(int start, int length)` Get a subsequence of the value
`java.lang.String`	`toString()` Returns a string representation of the object (used only for diagnostics).

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface net.sf.saxon.om.GroundedValue
asIterable, concatenate, containsNode, materialize, toShortString

Methods inherited from interface net.sf.saxon.om.Sequence
makeRepeatable

- 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
  - iterate
```
public SequenceIterator iterate()
```
    Return an iterator over this value.
    
    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.
  - 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

Class ZeroOrOne<T extends Item>

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Methods inherited from interface net.sf.saxon.om.GroundedValue

Methods inherited from interface net.sf.saxon.om.Sequence

Constructor Detail

ZeroOrOne

Method Detail

empty

getUnicodeStringValue

getStringValue

head

getLength

itemAt

subsequence

iterate

effectiveBooleanValue

toString

reduce