org.apache.commons.collections4.iterators

Class PushbackIterator<E>

java.lang.Object

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

All Implemented Interfaces:

java.util.Iterator<E>

public class PushbackIterator<E>
extends java.lang.Object
implements java.util.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 and Description
PushbackIterator(java.util.Iterator<? extends E> iterator) Constructor.

Method Summary

Modifier and Type	Method and Description
boolean	hasNext()
E	next()
void	pushback(E item) Push back the given element to the iterator.
static <E> PushbackIterator<E>	pushbackIterator(java.util.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

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

Methods inherited from interface java.util.Iterator

forEachRemaining

Constructor Detail

PushbackIterator

public PushbackIterator(java.util.Iterator<? extends E> iterator)

Constructor.

Parameters:

iterator - the iterator to decorate

Method Detail

pushbackIterator

public static <E> PushbackIterator<E> pushbackIterator(java.util.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:

java.lang.NullPointerException - 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 java.util.Iterator<E>

next

public E next()

Specified by:

next in interface java.util.Iterator<E>

remove

public void remove()

This iterator will always throw an UnsupportedOperationException.

Specified by:

remove in interface java.util.Iterator<E>

Throws:

java.lang.UnsupportedOperationException - always