org.apache.commons.collections.iterators
Class IteratorChain

java.lang.Object
  org.apache.commons.collections.iterators.IteratorChain

All Implemented Interfaces:

java.util.Iterator

public class IteratorChain
extends java.lang.Object
implements java.util.Iterator

An IteratorChain is an Iterator that wraps a number of Iterators.

This class makes multiple iterators look like one to the caller When any method from the Iterator interface is called, the IteratorChain will delegate to a single underlying Iterator. The IteratorChain will invoke the Iterators in sequence until all Iterators are exhausted.

Under many circumstances, linking Iterators together in this manner is more efficient (and convenient) than reading out the contents of each Iterator into a List and creating a new Iterator.

Calling a method that adds new Iteratorafter a method in the Iterator interface has been called will result in an UnsupportedOperationException. Subclasses should take care to not alter the underlying List of Iterators.

NOTE: As from version 3.0, the IteratorChain may contain no iterators. In this case the class will function as an empty iterator.

Since:

Commons Collections 2.1

Version:

$Revision: 647116 $ $Date: 2008-04-11 12:23:08 +0100 (Fri, 11 Apr 2008) $

Author:

Morgan Delagrange, Stephen Colebourne

Field Summary

protected java.util.Iterator	currentIterator The current iterator
protected int	currentIteratorIndex The index of the current iterator
protected boolean	isLocked ComparatorChain is "locked" after the first time compare(Object,Object) is called
protected java.util.List	iteratorChain The chain of iterators
protected java.util.Iterator	lastUsedIterator The "last used" Iterator is the Iterator upon which next() or hasNext() was most recently called used for the remove() operation only

Constructor Summary

IteratorChain()
Construct an IteratorChain with no Iterators.

IteratorChain(java.util.Collection iterators)
Constructs a new IteratorChain over the collection of iterators.

IteratorChain(java.util.Iterator iterator)
Construct an IteratorChain with a single Iterator.

IteratorChain(java.util.Iterator[] iterators)
Constructs a new IteratorChain over the array of iterators.

IteratorChain(java.util.Iterator a, java.util.Iterator b)
Constructs a new IteratorChain over the two given iterators.

Method Summary

void	addIterator(java.util.Iterator iterator) Add an Iterator to the end of the chain
java.util.List	getIterators() Get the list of Iterators (unmodifiable)
boolean	hasNext() Return true if any Iterator in the IteratorChain has a remaining element.
boolean	isLocked() Determine if modifications can still be made to the IteratorChain.
java.lang.Object	next() Returns the next Object of the current Iterator
void	remove() Removes from the underlying collection the last element returned by the Iterator.
void	setIterator(int index, java.util.Iterator iterator) Set the Iterator at the given index
int	size() Number of Iterators in the current IteratorChain.
protected void	updateCurrentIterator() Updates the current iterator field to ensure that the current Iterator is not exhausted

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

iteratorChain

protected final java.util.List iteratorChain

The chain of iterators

currentIteratorIndex

protected int currentIteratorIndex

The index of the current iterator

currentIterator

protected java.util.Iterator currentIterator

The current iterator

lastUsedIterator

protected java.util.Iterator lastUsedIterator

The "last used" Iterator is the Iterator upon which next() or hasNext() was most recently called used for the remove() operation only

isLocked

protected boolean isLocked

ComparatorChain is "locked" after the first time compare(Object,Object) is called

Constructor Detail

IteratorChain

public IteratorChain()

Construct an IteratorChain with no Iterators.

You will normally use addIterator(Iterator) to add some iterators after using this constructor.

IteratorChain

public IteratorChain(java.util.Iterator iterator)

Construct an IteratorChain with a single Iterator.

Parameters:

iterator - first Iterator in the IteratorChain

Throws:

java.lang.NullPointerException - if the iterator is null

IteratorChain

public IteratorChain(java.util.Iterator a,
                     java.util.Iterator b)

Constructs a new IteratorChain over the two given iterators.

Parameters:

a - the first child iterator

b - the second child iterator

Throws:

java.lang.NullPointerException - if either iterator is null

IteratorChain

public IteratorChain(java.util.Iterator[] iterators)

Constructs a new IteratorChain over the array of iterators.

Parameters:

iterators - the array of iterators

Throws:

java.lang.NullPointerException - if iterators array is or contains null

IteratorChain

public IteratorChain(java.util.Collection iterators)

Constructs a new IteratorChain over the collection of iterators.

Parameters:

iterators - the collection of iterators

Throws:

java.lang.NullPointerException - if iterators collection is or contains null

java.lang.ClassCastException - if iterators collection doesn't contain an iterator

Method Detail

addIterator

public void addIterator(java.util.Iterator iterator)

Add an Iterator to the end of the chain

Parameters:

iterator - Iterator to add

Throws:

java.lang.IllegalStateException - if I've already started iterating

java.lang.NullPointerException - if the iterator is null

setIterator

public void setIterator(int index,
                        java.util.Iterator iterator)
                 throws java.lang.IndexOutOfBoundsException

Set the Iterator at the given index

Parameters:

index - index of the Iterator to replace

iterator - Iterator to place at the given index

Throws:

java.lang.IndexOutOfBoundsException - if index < 0 or index > size()

java.lang.IllegalStateException - if I've already started iterating

java.lang.NullPointerException - if the iterator is null

getIterators

public java.util.List getIterators()

Get the list of Iterators (unmodifiable)

Returns:

the unmodifiable list of iterators added

size

public int size()

Number of Iterators in the current IteratorChain.

Returns:

Iterator count

isLocked

public boolean isLocked()

Determine if modifications can still be made to the IteratorChain. IteratorChains cannot be modified once they have executed a method from the Iterator interface.

Returns:

true if IteratorChain cannot be modified, false if it can

updateCurrentIterator

protected void updateCurrentIterator()

Updates the current iterator field to ensure that the current Iterator is not exhausted

hasNext

public boolean hasNext()

Return true if any Iterator in the IteratorChain has a remaining element.

Specified by:

hasNext in interface java.util.Iterator

Returns:

true if elements remain

next

public java.lang.Object next()

Returns the next Object of the current Iterator

Specified by:

next in interface java.util.Iterator

Returns:

Object from the current Iterator

Throws:

java.util.NoSuchElementException - if all the Iterators are exhausted

remove

public void remove()

Removes from the underlying collection the last element returned by the Iterator. As with next() and hasNext(), this method calls remove() on the underlying Iterator. Therefore, this method may throw an UnsupportedOperationException if the underlying Iterator does not support this method.

Specified by:

remove in interface java.util.Iterator

Throws:

java.lang.UnsupportedOperationException - if the remove operator is not supported by the underlying Iterator

java.lang.IllegalStateException - if the next method has not yet been called, or the remove method has already been called after the last call to the next method.