Empty

java.lang.Object
- org.basex.data.ExprInfo
- - org.basex.query.expr.Expr
  - - org.basex.query.item.Value
    - - org.basex.query.item.Empty

All Implemented Interfaces:

java.lang.Iterable<Item>
```
public final class Empty
extends Value
```
Empty sequence.

Author:

BaseX Team 2005-12, BSD License, Christian Gruen

Nested Class Summary
- Nested classes/interfaces inherited from class org.basex.query.expr.Expr
  Expr.Use

Field Summary

Fields
Modifier and Type Field and Description

static ValueIter ITER
Empty iterator.

static Empty SEQ
Single instance.
- Fields inherited from class org.basex.query.item.Value
  type

Fields
Modifier and Type	Field and Description
`static ValueIter`	`ITER` Empty iterator.
`static Empty`	`SEQ` Single instance.

Method Summary

Methods
Modifier and Type	Method and Description
`Item`	`ebv(QueryContext ctx, InputInfo ii)` Checks if the iterator can be dissolved into an effective boolean value.
`int`	`hash(InputInfo ii)` Returns a hash code for this value.
`boolean`	`homogenous()` Checks if all items of this value share the same type.
`boolean`	`isEmpty()` Tests if this is an empty sequence.
`boolean`	`isVacuous()` Tests if this is a vacuous expression (empty sequence or error function).
`Item`	`item(QueryContext ctx, InputInfo ii)` Evaluates the expression and returns the resulting item or a `null` reference, if the expression yields an empty sequence.
`Item`	`itemAt(long pos)` Gets the item at the given position in the value.
`ValueIter`	`iter()` Returns an iterator.
`boolean`	`iterable()` Returns true if the expression is iterable, i.e., if it does not contain any duplicates and if all results are sorted.
`void`	`plan(Serializer ser)` Serializes the expression tree.
`long`	`size()` Returns the sequence size or 1.
`Item`	`test(QueryContext ctx, InputInfo ii)` Performs a predicate test and returns the item if test was successful.
`java.lang.Object`	`toJava()` Returns a Java representation of the value.
`java.lang.String`	`toString()`
`SeqType`	`type()` Returns the sequence type of the evaluated value.
`int`	`writeTo(Item[] arr, int start)` Writes this value's items out to the given array.

Methods inherited from class org.basex.query.item.Value
cache, comp, count, data, description, info, isValue, iter, iterator, removable, remove, uses, value

Methods inherited from class org.basex.query.expr.Expr
addText, compEbv, hasFreeVars, indexAccessible, indexEquivalent, isFunction, isItem, markTailCalls, sameAs

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

- Field Detail
  - SEQ
```
public static final Empty SEQ
```
    Single instance.
  - ITER
```
public static final ValueIter ITER
```
    Empty iterator.
- Method Detail
  - isEmpty
```
public boolean isEmpty()
```
    Description copied from class: Expr
    
    Tests if this is an empty sequence. This function is only overwritten by the Empty class, which represents the empty sequence.
    
    Overrides:
    
    isEmpty in class Expr
    
    Returns:
    result of check
  - isVacuous
```
public boolean isVacuous()
```
    Description copied from class: Expr
    
    Tests if this is a vacuous expression (empty sequence or error function). This check is needed for updating queries.
    
    Overrides:
    
    isVacuous in class Expr
    
    Returns:
    result of check
  - size
```
public long size()
```
    Description copied from class: Expr
    
    Returns the sequence size or 1.
    
    Specified by:
    
    size in class Value
    
    Returns:
    result of check
  - toJava
```
public java.lang.Object toJava()
```
    Description copied from class: Value
    
    Returns a Java representation of the value.
    
    Specified by:
    
    toJava in class Value
    
    Returns:
    Java object
  - iter
```
public ValueIter iter()
```
    Description copied from class: Value
    
    Returns an iterator.
    
    Specified by:
    
    iter in class Value
    
    Returns:
    iterator
  - item
```
public Item item(QueryContext ctx,
        InputInfo ii)
```
    Description copied from class: Expr
    
    Evaluates the expression and returns the resulting item or a null reference, if the expression yields an empty sequence. If this method is not overwritten, Expr.iter(org.basex.query.QueryContext) must be implemented by an expression, as it may be called by this method.
    
    Specified by:
    
    item in class Expr
    
    Parameters:
    ctx - query context
    ii - input info
    
    Returns:
    iterator
  - ebv
```
public Item ebv(QueryContext ctx,
       InputInfo ii)
```
    Description copied from class: Expr
    
    Checks if the iterator can be dissolved into an effective boolean value. If not, returns an error. If yes, returns the first value - which can be also be e.g. an integer, which is later evaluated as numeric predicate.
    
    Specified by:
    
    ebv in class Expr
    
    Parameters:
    ctx - query context
    ii - input info
    
    Returns:
    item
  - test
```
public Item test(QueryContext ctx,
        InputInfo ii)
```
    Description copied from class: Expr
    
    Performs a predicate test and returns the item if test was successful.
    
    Specified by:
    
    test in class Expr
    
    Parameters:
    ctx - query context
    ii - input info
    
    Returns:
    item
  - type
```
public SeqType type()
```
    Description copied from class: Expr
    
    Returns the sequence type of the evaluated value. For simplicity, some types have been summarized. E.g., all numbers are treated as integers.
    
    Specified by:
    
    type in class Expr
    
    Returns:
    result of check
  - iterable
```
public boolean iterable()
```
    Description copied from class: Expr
    
    Returns true if the expression is iterable, i.e., if it does not contain any duplicates and if all results are sorted. This method is called e.g. by AxisPath.
    
    Overrides:
    
    iterable in class Expr
    
    Returns:
    result of check
  - plan
```
public void plan(Serializer ser)
          throws java.io.IOException
```
    Description copied from class: ExprInfo
    
    Serializes the expression tree.
    
    Specified by:
    
    plan in class ExprInfo
    
    Parameters:
    ser - serializer
    
    Throws:
    
    java.io.IOException - I/O exception
  - hash
```
public int hash(InputInfo ii)
```
    Description copied from class: Value
    
    Returns a hash code for this value.
    
    Specified by:
    
    hash in class Value
    
    Parameters:
    ii - input info
    
    Returns:
    hash code
  - toString
```
public java.lang.String toString()
```
    Specified by:
    
    toString in class ExprInfo
  - writeTo
```
public int writeTo(Item[] arr,
          int start)
```
    Description copied from class: Value
    
    Writes this value's items out to the given array.
    
    Specified by:
    
    writeTo in class Value
    
    Parameters:
    arr - array to write to
    start - start position
    
    Returns:
    number of written items
  - itemAt
```
public Item itemAt(long pos)
```
    Description copied from class: Value
    
    Gets the item at the given position in the value.
    
    Specified by:
    
    itemAt in class Value
    
    Parameters:
    pos - position
    
    Returns:
    item
  - homogenous
```
public boolean homogenous()
```
    Description copied from class: Value
    
    Checks if all items of this value share the same type.
    
    Specified by:
    
    homogenous in class Value
    
    Returns:
    result of check

Class Empty

Nested Class Summary

Nested classes/interfaces inherited from class org.basex.query.expr.Expr

Field Summary

Fields inherited from class org.basex.query.item.Value

Method Summary

Methods inherited from class org.basex.query.item.Value

Methods inherited from class org.basex.query.expr.Expr

Methods inherited from class java.lang.Object

Field Detail

SEQ

ITER

Method Detail

isEmpty

isVacuous

size

toJava

iter

item

ebv

test

type

iterable

plan

hash

toString

writeTo

itemAt

homogenous