Chain

java.lang.Object
- net.sf.saxon.om.Chain

All Implemented Interfaces:

GroundedValue, Sequence
```
public class Chain
extends Object
implements GroundedValue
```
A chain is an implementation of Sequence that represents the concatenation of a number of subsequences.
The most common use case is a recursive function that appends one item to a sequence each time it is called. Each call of this function will create a Chain with two subsequences, the first being a Chain and the second an individual item. The design of the class is constrained by the need to handle this extreme case.

Firstly, the iterator for the class cannot use simple recursion to navigate the tree because it will often be too deep, causing StackOverflow. So it maintains its own Stack (on the Java heap).

Secondly, even using the heap will run out of space at about a million entries. To prevent this, any Chains of size less than thirty items are amalgamated into chunks of 30. Building larger chunks than this would cause insertion operations to have linear performance (and thus the total cost of sequence construction would be quadratic. The figure of 30 was chosen because elapsed time is almost as good as with smaller chunks, and memory use during navigation is substantially reduced.

Constructor Summary

Constructors
Constructor and Description

Chain(List<GroundedValue> children)

Constructors
Constructor and Description
`Chain(List<GroundedValue> children)`

Method Summary

Methods
Modifier and Type	Method and Description
`void`	`append(GroundedValue sequence)` Add more items to the end of this sequence.
`void`	`append(Item item)` Add a single item to the end of this sequence.
`boolean`	`effectiveBooleanValue()` Get the effective boolean value of this sequence
`int`	`getLength()` Get the size of the value (the number of items)
`String`	`getStringValue()` Get the string value of this sequence.
`CharSequence`	`getStringValueCS()` Get the string value of this sequence.
`Item`	`head()` Get the first item in the sequence.
`Item`	`itemAt(int n)` Get the n'th item in the value, counting from 0
`SequenceIterator<Item>`	`iterate()` Get an iterator performance characteristics, though all should exhibit the same behaviour.over all the items in the sequence
`GroundedValue`	`reduce()` Reduce the sequence to its simplest form.
`GroundedValue`	`subsequence(int start, int length)` Get a subsequence of the value

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

- Constructor Detail
  - Chain
```
public Chain(List<GroundedValue> children)
```
- Method Detail
  - head
```
public Item head()
          throws XPathException
```
    Description copied from interface: Sequence
    
    Get the first item in the sequence.
    
    Specified by:
    
    head in interface Sequence
    
    Returns:
    the first item in the sequence if there is one, or null if the sequence is empty
    
    Throws:
    
    XPathException - in the situation where the sequence is evaluated lazily, and evaluation of the first item causes a dynamic error.
  - iterate
```
public SequenceIterator<Item> iterate()
```
    Description copied from interface: Sequence
    
    Get an iterator performance characteristics, though all should exhibit the same behaviour.over all the items in the sequence
    
    Specified by:
    
    iterate in interface Sequence
    
    Returns:
    an iterator over all the items
  - append
```
public void append(GroundedValue sequence)
```
    Add more items to the end of this sequence. This method must only be called while the value is being constructed, since the sequence thereafter is immutable.
    
    Parameters:
    sequence - the items to be added
  - append
```
public void append(Item item)
```
    Add a single item to the end of this sequence. This method must only be called while the value is being constructed, since the sequence thereafter is immutable.
    
    Parameters:
    item - the item to be added
  - itemAt
```
public Item itemAt(int n)
```
    Get the n'th item in the value, counting from 0
    
    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.
  - getLength
```
public int getLength()
```
    Get the size of the value (the number of items)
    
    Specified by:
    
    getLength in interface GroundedValue
    
    Returns:
    the number of items in the sequence
  - effectiveBooleanValue
```
public boolean effectiveBooleanValue()
                              throws XPathException
```
    Get the effective boolean value of this sequence
    
    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)
  - getStringValue
```
public String getStringValue()
                      throws XPathException
```
    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.
    
    Throws:
    
    XPathException - if the sequence contains items that have no string value (for example, function items)
  - getStringValueCS
```
public CharSequence getStringValueCS()
                              throws XPathException
```
    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.
    
    Throws:
    
    XPathException - if the sequence contains items that have no string value (for example, function items)
  - 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 Chain

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

Chain

Method Detail

head

iterate

append

append

itemAt

subsequence

getLength

effectiveBooleanValue

getStringValue

getStringValueCS

reduce