PermutationIterator (Apache Commons Collections 4.2 API)

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> coll)
Standard constructor for this class.

Method Summary

All Methods Instance Methods Concrete Methods
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()`

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 Detail
  - PermutationIterator
```
public PermutationIterator(Collection<? extends E> coll)
```
    Standard constructor for this class.
    
    Parameters:
    
    coll - the collection to generate permutations for
    
    Throws:
    
    NullPointerException - if coll is null
- Method Detail
  - 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()
```
    Specified by:
    
    remove in interface Iterator<E>