org.apache.commons.collections4.iterators
Class PushbackIterator<E>

java.lang.Object
  org.apache.commons.collections4.iterators.PushbackIterator<E>

All Implemented Interfaces:

Iterator<E>

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

Decorates an iterator to support pushback of elements.

The decorator stores the pushed back elements in a LIFO manner: the last element that has been pushed back, will be returned as the next element in a call to next().

The decorator does not support the removal operation. Any call to remove() will result in an UnsupportedOperationException.

Since:

4.0

Version:

$Id: PushbackIterator.java 1479763 2013-05-07 05:28:39Z tn $

PushbackIterator

public PushbackIterator(Iterator<? extends E> iterator)

Constructor.

Parameters:

iterator - the iterator to decorate

pushbackIterator

public static <E> PushbackIterator<E> pushbackIterator(Iterator<? extends E> iterator)

Decorates the specified iterator to support one-element lookahead.

If the iterator is already a PeekingIterator it is returned directly.

Type Parameters:

E - the element type

Parameters:

iterator - the iterator to decorate

Returns:

a new peeking iterator

Throws:

IllegalArgumentException - if the iterator is null

pushback

public void pushback(E item)

Push back the given element to the iterator.

Calling next() immediately afterwards will return exactly this element.

Parameters:

item - the element to push back to the iterator

hasNext

public boolean hasNext()

Specified by:

hasNext in interface Iterator<E>

next

public E next()

Specified by:

next in interface Iterator<E>

remove

public void remove()

This iterator will always throw an UnsupportedOperationException.

Specified by:

remove in interface Iterator<E>

Throws:

UnsupportedOperationException - always