Package org.apache.commons.collections4.iterators

Class CollatingIterator<E>

java.lang.Object

org.apache.commons.collections4.iterators.CollatingIterator<E>

Type Parameters:

E - the type of elements returned by this iterator.

All Implemented Interfaces:

Iterator<E>

public class CollatingIterator<E>
extends Object
implements Iterator<E>

Provides an ordered iteration over the elements contained in a collection of ordered Iterators.

Given two ordered Iterator instances A and B, the next() method on this iterator will return the lesser of A.next() and B.next().

Since:

2.1

Constructor Summary

Constructors

Constructor	Description
CollatingIterator()	Constructs a new CollatingIterator.
CollatingIterator(Comparator<? super E> comp)	Constructs a new CollatingIterator that will use the specified comparator for ordering.
CollatingIterator(Comparator<? super E> comp, int initIterCapacity)	Constructs a new CollatingIterator that will use the specified comparator for ordering and have the specified initial capacity.
CollatingIterator(Comparator<? super E> comp, Collection<Iterator<? extends E>> iterators)	Constructs a new CollatingIterator that will use the specified comparator to provide ordered iteration over the collection of iterators.
CollatingIterator(Comparator<? super E> comp, Iterator<? extends E>[] iterators)	Constructs a new CollatingIterator that will use the specified comparator to provide ordered iteration over the array of iterators.
CollatingIterator(Comparator<? super E> comp, Iterator<? extends E> a, Iterator<? extends E> b)	Constructs a new CollatingIterator that will use the specified comparator to provide ordered iteration over the two given iterators.

Method Summary

Modifier and Type	Method	Description
void	addIterator(Iterator<? extends E> iterator)	Adds the given Iterator to the iterators being collated.
Comparator<? super E>	getComparator()	Gets the Comparator by which collation occurs.
int	getIteratorIndex()	Returns the index of the iterator that returned the last element.
List<Iterator<? extends E>>	getIterators()	Gets the list of Iterators (unmodifiable).
boolean	hasNext()	Returns true if any child iterator has remaining elements.
E	next()	Returns the next ordered element from a child iterator.
void	remove()	Removes the last returned element from the child iterator that produced it.
void	setComparator(Comparator<? super E> comp)	Sets the Comparator by which collation occurs.
void	setIterator(int index, Iterator<? extends E> iterator)	Sets the iterator at the given index.

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.Iterator

forEachRemaining

Constructor Details

CollatingIterator

public CollatingIterator()

Constructs a new CollatingIterator. A comparator must be set by calling setComparator(Comparator) before invoking hasNext(), or next() for the first time. Child iterators will have to be manually added using the addIterator(Iterator) method.

CollatingIterator

public CollatingIterator(Comparator<? super E> comp)

Constructs a new CollatingIterator that will use the specified comparator for ordering. Child iterators will have to be manually added using the addIterator(Iterator) method.

Parameters:

comp - the comparator to use to sort; must not be null, unless you'll be invoking setComparator(Comparator) later on.

CollatingIterator

public CollatingIterator(Comparator<? super E> comp,
 Collection<Iterator<? extends E>> iterators)

Constructs a new CollatingIterator that will use the specified comparator to provide ordered iteration over the collection of iterators.

Parameters:

comp - the comparator to use to sort; must not be null, unless you'll be invoking setComparator(Comparator) later on.

iterators - the collection of iterators

Throws:

NullPointerException - if the iterators collection is or contains null

ClassCastException - if the iterators collection contains an element that's not an Iterator

CollatingIterator

public CollatingIterator(Comparator<? super E> comp,
 int initIterCapacity)

Constructs a new CollatingIterator that will use the specified comparator for ordering and have the specified initial capacity. Child iterators will have to be manually added using the addIterator(Iterator) method.

Parameters:

comp - the comparator to use to sort; must not be null, unless you'll be invoking setComparator(Comparator) later on.

initIterCapacity - the initial capacity for the internal list of child iterators

CollatingIterator

public CollatingIterator(Comparator<? super E> comp,
 Iterator<? extends E> a,
 Iterator<? extends E> b)

Constructs a new CollatingIterator that will use the specified comparator to provide ordered iteration over the two given iterators.

Parameters:

comp - the comparator to use to sort; must not be null, unless you'll be invoking setComparator(Comparator) later on.

a - the first child ordered iterator

b - the second child ordered iterator

Throws:

NullPointerException - if either iterator is null

CollatingIterator

public CollatingIterator(Comparator<? super E> comp,
 Iterator<? extends E>[] iterators)

Constructs a new CollatingIterator that will use the specified comparator to provide ordered iteration over the array of iterators.

Parameters:

comp - the comparator to use to sort; must not be null, unless you'll be invoking setComparator(Comparator) later on.

iterators - the array of iterators

Throws:

NullPointerException - if iterators array is or contains null

Method Details

addIterator

public void addIterator(Iterator<? extends E> iterator)

Adds the given Iterator to the iterators being collated.

Parameters:

iterator - the iterator to add to the collation, must not be null

Throws:

IllegalStateException - if iteration has started

NullPointerException - if the iterator is null

getComparator

public Comparator<? super E> getComparator()

Gets the Comparator by which collation occurs.

Returns:

the Comparator

getIteratorIndex

public int getIteratorIndex()

Returns the index of the iterator that returned the last element.

Returns:

the index of the iterator that returned the last element

Throws:

IllegalStateException - if there is no last returned element

getIterators

public List<Iterator<? extends E>> getIterators()

Gets the list of Iterators (unmodifiable).

Returns:

the unmodifiable list of iterators added

hasNext

public boolean hasNext()

Returns true if any child iterator has remaining elements.

Specified by:

hasNext in interface Iterator<E>

Returns:

true if this iterator has remaining elements

next

public E next()
       throws NoSuchElementException

Returns the next ordered element from a child iterator.

Specified by:

next in interface Iterator<E>

Returns:

the next ordered element

Throws:

NoSuchElementException - if no child iterator has any more elements

remove

public void remove()

Removes the last returned element from the child iterator that produced it.

Specified by:

remove in interface Iterator<E>

Throws:

IllegalStateException - if there is no last returned element, or if the last returned element has already been removed

setComparator

public void setComparator(Comparator<? super E> comp)

Sets the Comparator by which collation occurs. If you would like to use the natural sort order (or, in other words, if the elements in the iterators are implementing the Comparable interface), then use the ComparableComparator.

Parameters:

comp - the Comparator to set

Throws:

IllegalStateException - if iteration has started

setIterator

public void setIterator(int index,
 Iterator<? extends E> iterator)

Sets 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 iteration has started

NullPointerException - if the iterator is null