Package org.apache.commons.collections4.iterators

Class PushbackIterator<E>

java.lang.Object

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

Type Parameters:

E - the type of elements returned by this iterator.

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

Constructor Summary

Constructors

Constructor	Description
PushbackIterator(Iterator<? extends E> iterator)	Constructs a new instance.

Method Summary

Modifier and Type	Method	Description
boolean	hasNext()
E	next()
void	pushback(E item)	Push back the given element to the iterator.
static <E> PushbackIterator<E>	pushbackIterator(Iterator<? extends E> iterator)	Decorates the specified iterator to support one-element lookahead.
void	remove()	This iterator will always throw an 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

PushbackIterator

public PushbackIterator(Iterator<? extends E> iterator)

Constructs a new instance.

Parameters:

iterator - the iterator to decorate

Method Details

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 PushbackIterator it is returned directly.

Type Parameters:

E - the element type

Parameters:

iterator - the iterator to decorate

Returns:

a new peeking iterator

Throws:

NullPointerException - if the iterator is null

hasNext

public boolean hasNext()

Specified by:

hasNext in interface Iterator<E>

next

public E next()

Specified by:

next in interface Iterator<E>

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

remove

public void remove()

This iterator will always throw an UnsupportedOperationException.

Specified by:

remove in interface Iterator<E>

Throws:

UnsupportedOperationException - always