org.apache.commons.collections.iterators

Class IteratorChain

public class IteratorChain extends Object implements 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: 171347 $ $Date: 2005-05-22 18:27:34 +0100 (Sun, 22 May 2005) $

Author: Morgan Delagrange Stephen Colebourne

Field Summary
protected IteratorcurrentIterator
The current iterator
protected intcurrentIteratorIndex
The index of the current iterator
protected booleanisLocked
ComparatorChain is "locked" after the first time compare(Object,Object) is called
protected ListiteratorChain
The chain of iterators
protected IteratorlastUsedIterator
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(Iterator iterator)
Construct an IteratorChain with a single Iterator.
IteratorChain(Iterator a, Iterator b)
Constructs a new IteratorChain over the two given iterators.
IteratorChain(Iterator[] iterators)
Constructs a new IteratorChain over the array of iterators.
IteratorChain(Collection iterators)
Constructs a new IteratorChain over the collection of iterators.
Method Summary
voidaddIterator(Iterator iterator)
Add an Iterator to the end of the chain
ListgetIterators()
Get the list of Iterators (unmodifiable)
booleanhasNext()
Return true if any Iterator in the IteratorChain has a remaining element.
booleanisLocked()
Determine if modifications can still be made to the IteratorChain.
Objectnext()
Returns the next Object of the current Iterator
voidremove()
Removes from the underlying collection the last element returned by the Iterator.
voidsetIterator(int index, Iterator iterator)
Set the Iterator at the given index
intsize()
Number of Iterators in the current IteratorChain.
protected voidupdateCurrentIterator()
Updates the current iterator field to ensure that the current Iterator is not exhausted

Field Detail

currentIterator

protected Iterator currentIterator
The current iterator

currentIteratorIndex

protected int currentIteratorIndex
The index of the current iterator

isLocked

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

iteratorChain

protected final List iteratorChain
The chain of iterators

lastUsedIterator

protected 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 Detail

IteratorChain

public IteratorChain()
Construct an IteratorChain with no Iterators.

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

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 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

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(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

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

Returns: true if elements remain

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

next

public Object next()
Returns the next Object of the current 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.

Throws: UnsupportedOperationException if the remove operator is not supported by the underlying Iterator 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)
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()
Updates the current iterator field to ensure that the current Iterator is not exhausted
Copyright © 2001-2008 Apache Software Foundation. All Rights Reserved.