EmptySequence

java.lang.Object
- net.sf.saxon.value.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 Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`boolean`	`effectiveBooleanValue()` Get the effective boolean value - always false
`boolean`	`equals(java.lang.Object other)` Is this expression the same as another expression?
`static EmptySequence`	`getInstance()` Get the implicit instance of this class
`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()` Get the string value of this sequence, as an instance of `UnicodeString`.
`int`	`hashCode()`
`Item`	`head()` Get the first item in the sequence.
`Item`	`itemAt(int n)` Get the n'th item in the sequence (starting from 0).
`SequenceIterator`	`iterate()` Return an iteration over the sequence
`GroundedValue`	`reduce()` Reduce the sequence to its simplest form.
`GroundedValue`	`subsequence(int min, int length)` Get a subsequence of the value
`java.lang.String`	`toString()` Returns a string representation of the object.

Methods inherited from class java.lang.Object
clone, finalize, getClass, 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

- 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
  - iterate
```
public SequenceIterator iterate()
```
    Return an iteration over the sequence
    
    Specified by:
    
    iterate in interface GroundedValue
    
    Specified by:
    
    iterate in interface Sequence
    
    Returns:
    
    an empty iterator
  - 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

Class EmptySequence

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

Method Detail

getInstance

getUnicodeStringValue

getStringValue

head

iterate

getLength

equals

hashCode

effectiveBooleanValue

itemAt

subsequence

toString

reduce