org.apache.commons.collections.iterators
Class IteratorChain

java.lang.Object
  |
  +--org.apache.commons.collections.iterators.IteratorChain

All Implemented Interfaces:

Iterator

public class IteratorChain

extends Object

implements Iterator

An IteratorChain is an Iterator that wraps one or more Iterators. When any method from the Iterator interface is called, the IteratorChain will proxy to a single underlying Iterator. The IteratorChain will invoke the Iterators in sequence until all Iterators are exhausted completely.

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.

Since:

2.1

Version:

$Id: IteratorChain.java,v 1.2 2002/08/17 11:28:36 scolebourne Exp $

Author:

Morgan Delagrange, Stephen Colebourne

Field Summary

protected Iterator	currentIterator
protected int	currentIteratorIndex
protected boolean	isLocked
protected List	iteratorChain
protected Iterator	lastUsedIterator

Constructor Summary

IteratorChain()
Construct an IteratorChain with no Iterators.

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

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

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

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

Method Summary

void	addIterator(Iterator iterator) Add an Iterator to the end of the chain
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.
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, Iterator iterator) Set the Iterator at the given index
int	size() Number of Iterators in the current IteratorChain.
protected void	updateCurrentIterator()

Methods inherited from class java.lang.Object

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

Field Detail

currentIterator

protected Iterator currentIterator

currentIteratorIndex

protected int currentIteratorIndex

isLocked

protected boolean isLocked

iteratorChain

protected final List iteratorChain

lastUsedIterator

protected Iterator lastUsedIterator

Constructor Detail

IteratorChain

public IteratorChain()

Construct an IteratorChain with no Iterators. You must add at least Iterator before calling any method from the Iterator interface, or an UnsupportedOperationException is thrown

IteratorChain

public IteratorChain(Collection iterators)

Constructs a new IteratorChain over the collection of iterators.

Parameters:

iterators - the collection of iterators

Throws:

NullPointerException - if iterators collection is or contains null

ClassCastException - if iterators collection doesn't contain an iterator

IteratorChain

public IteratorChain(Iterator iterator)

Construct an IteratorChain with a single Iterator.

Parameters:

iterator - first Iterator in the IteratorChain

Throws:

NullPointerException - if the iterator is null

IteratorChain

public IteratorChain(Iterator[] iterators)

Constructs a new IteratorChain over the array of iterators.

Parameters:

iterators - the array of iterators

Throws:

NullPointerException - if iterators array is or contains null

IteratorChain

public IteratorChain(Iterator a,
                     Iterator b)

Constructs a new IteratorChain over the two given iterators.

Parameters:

a - the first child iterator

b - the second child iterator

Throws:

NullPointerException - if either iterator is null

Method Detail

addIterator

public void addIterator(Iterator iterator)

Add an Iterator to the end of the chain

Parameters:

iterator - Iterator to add

Throws:

IllegalStateException - if I've already started iterating

NullPointerException - if the iterator is null

getIterators

public List getIterators()

Get the list of Iterators (unmodifiable)

Returns:

the unmodifiable list of iterators added

hasNext

public boolean hasNext()
                throws UnsupportedOperationException

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

Specified by:

hasNext in interface Iterator

Returns:

true if elements remain

Throws:

UnsupportedOperationException - if the IteratorChain does not contain at least one Iterator

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 = IteratorChain cannot be modified; false = IteratorChain can still be modified.

next

public Object next()
            throws NoSuchElementException,
                   UnsupportedOperationException

Returns the next Object of the current Iterator

Specified by:

next in interface Iterator

Returns:

Object from the current Iterator

Throws:

NoSuchElementException - if all the Iterators are exhausted

UnsupportedOperationException - if the IteratorChain does not contain at least one Iterator

remove

public void remove()
            throws UnsupportedOperationException,
                   IllegalStateException

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 Iterator

Throws:

UnsupportedOperationException - if the remove operator is not supported by the underlying Iterator or if there are no Iterators in the IteratorChain

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.

setIterator

public void setIterator(int index,
                        Iterator iterator)
                 throws 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:

IndexOutOfBoundsException - if index < 0 or index > size()

IllegalStateException - if I've already started iterating

NullPointerException - if the iterator is null

size

public int size()

Number of Iterators in the current IteratorChain.

Returns:

Iterator count

updateCurrentIterator

protected void updateCurrentIterator()