Package org.apache.commons.collections4.iterators

Class PermutationIterator<E>

java.lang.Object

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

Type Parameters:

E - the type of the objects being permuted

All Implemented Interfaces:

Iterator<List<E>>

public class PermutationIterator<E>
extends Object
implements Iterator<List<E>>

This iterator creates permutations of an input collection, using the Steinhaus-Johnson-Trotter algorithm (also called plain changes).

The iterator will return exactly n! permutations of the input collection. The remove() operation is not supported, and will throw an UnsupportedOperationException.

NOTE: in case an empty collection is provided, the iterator will return exactly one empty list as result, as 0! = 1.

Since:

4.0

Constructor Summary

Constructors

Constructor	Description
PermutationIterator(Collection<? extends E> collection)	Standard constructor for this class.

Method Summary

Modifier and Type	Method	Description
boolean	hasNext()	Indicates if there are more permutation available.
List<E>	next()	Returns the next permutation of the input collection.
void	remove()	Always throws UnsupportedOperationException.

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

PermutationIterator

public PermutationIterator(Collection<? extends E> collection)

Standard constructor for this class.

Parameters:

collection - The collection to generate permutations for

Throws:

NullPointerException - if coll is null

Method Details

hasNext

public boolean hasNext()

Indicates if there are more permutation available.

Specified by:

hasNext in interface Iterator<E>

Returns:

true if there are more permutations, otherwise false

next

public List<E> next()

Returns the next permutation of the input collection.

Specified by:

next in interface Iterator<E>

Returns:

A list of the permutator's elements representing a permutation

Throws:

NoSuchElementException - if there are no more permutations

remove

public void remove()

Always throws UnsupportedOperationException.

Specified by:

remove in interface Iterator<E>

Throws:

UnsupportedOperationException - Always thrown.