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org.apache.commons.collections.iterators

Class IteratorChain

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

All Implemented Interfaces:
Iterator


public class IteratorChain
extends java.lang.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
Authors:
Morgan Delagrange
Stephen Colebourne

Field Summary

Iterator

currentIterator

The current iterator

int

currentIteratorIndex

The index of the current iterator

boolean

isLocked

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

List

iteratorChain

The chain of iterators

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(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

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.

void

updateCurrentIterator()

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

Field Details

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 Details

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(Collection iterators)

Constructs a new IteratorChain over the collection of iterators.

Parameters:
iterators - the collection of iterators
Throws:
- if iterators collection is or contains null
- if iterators collection doesn't contain an iterator

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:
- if either iterator is null

IteratorChain

public IteratorChain(Iterator iterator)

Construct an IteratorChain with a single Iterator.

Parameters:
iterator - first Iterator in the IteratorChain
Throws:
- 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:
- if iterators array is or contains null

Method Details

addIterator

public void addIterator(Iterator iterator)

Add an Iterator to the end of the chain

Parameters:
iterator - Iterator to add
Throws:
- if I've already started iterating
- 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:
- 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:
- if the remove operator is not supported by the underlying Iterator
- 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:
- if index < 0 or index > size()
- if I've already started iterating
- 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