Class PeekingIterator<E>
java.lang.Object
org.apache.commons.collections4.iterators.PeekingIterator<E>
- All Implemented Interfaces:
Iterator<E>
Decorates an iterator to support one-element lookahead while iterating.
The decorator supports the removal operation, but an IllegalStateException
will be thrown if remove()
is called directly after a call to
peek()
or element()
.
- Since:
- 4.0
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Field Summary
FieldsModifier and TypeFieldDescriptionprivate boolean
Indicates that the decorated iterator is exhausted.The iterator being decorated.private E
The current slot for lookahead.private boolean
Indicates if the lookahead slot is filled. -
Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionelement()
Returns the next element in iteration without advancing the underlying iterator.private void
fill()
boolean
hasNext()
next()
peek()
Returns the next element in iteration without advancing the underlying iterator.static <E> PeekingIterator
<E> peekingIterator
(Iterator<? extends E> iterator) Decorates the specified iterator to support one-element lookahead.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
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Field Details
-
iterator
The iterator being decorated. -
exhausted
private boolean exhaustedIndicates that the decorated iterator is exhausted. -
slotFilled
private boolean slotFilledIndicates if the lookahead slot is filled. -
slot
The current slot for lookahead.
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Constructor Details
-
PeekingIterator
Constructor.- Parameters:
iterator
- the iterator to decorate
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-
Method Details
-
peekingIterator
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:
NullPointerException
- if the iterator is null
-
fill
private void fill() -
hasNext
public boolean hasNext() -
peek
Returns the next element in iteration without advancing the underlying iterator. If the iterator is already exhausted, null will be returned.Note: this method does not throw a
NoSuchElementException
if the iterator is already exhausted. If you want such a behavior, useelement()
instead.The rationale behind this is to follow the
Queue
interface which uses the same terminology.- Returns:
- the next element from the iterator
-
element
Returns the next element in iteration without advancing the underlying iterator. If the iterator is already exhausted, null will be returned.- Returns:
- the next element from the iterator
- Throws:
NoSuchElementException
- if the iterator is already exhausted according tohasNext()
-
next
-
remove
public void remove()
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