Interface Iterator<E>

Type Parameters:
E - the type of elements returned by this iterator
All Known Subinterfaces:
EventIterator, ListIterator<E>, PrimitiveIterator<T,​T_CONS>, PrimitiveIterator.OfDouble, PrimitiveIterator.OfInt, PrimitiveIterator.OfLong, XMLEventReader
All Known Implementing Classes:
BeanContextSupport.BCSIterator, EventReaderDelegate, Scanner 
public interface Iterator<E>

An iterator over a collection. Iterator takes the place of Enumeration in the Java Collections Framework. Iterators differ from enumerations in two ways:

  • Iterators allow the caller to remove elements from the underlying collection during the iteration with well-defined semantics.
  • Method names have been improved.

This interface is a member of the Java Collections Framework.

API Note:
An Enumeration can be converted into an Iterator by using the Enumeration.asIterator() method.
Since:
1.2
See Also:
Collection, ListIterator, Iterable

Methods

Modifier and Type Method Description
default void forEachRemaining​(Consumer<? super E> action)

Performs the given action for each remaining element until all elements have been processed or the action throws an exception.
boolean hasNext()

Returns true if the iteration has more elements.
E next()

Returns the next element in the iteration.
default void remove()

Removes from the underlying collection the last element returned by this iterator (optional operation).

Methods

hasNext

boolean hasNext()

Returns true if the iteration has more elements. (In other words, returns true if next() would return an element rather than throwing an exception.)

Returns:
true if the iteration has more elements

next

E next()

Returns the next element in the iteration.

Returns:
the next element in the iteration
Throws:
NoSuchElementException - if the iteration has no more elements

remove

default void remove()

Removes from the underlying collection the last element returned by this iterator (optional operation). This method can be called only once per call to next().

The behavior of an iterator is unspecified if the underlying collection is modified while the iteration is in progress in any way other than by calling this method, unless an overriding class has specified a concurrent modification policy.

The behavior of an iterator is unspecified if this method is called after a call to the forEachRemaining method.

Implementation Requirements:
The default implementation throws an instance of UnsupportedOperationException and performs no other action.
Throws:
UnsupportedOperationException - if the remove operation is not supported by this iterator
IllegalStateException - if the next method has not yet been called, or the remove method has already been called after the last call to the next method

forEachRemaining

default void forEachRemaining(Consumer<? super E> action)

Performs the given action for each remaining element until all elements have been processed or the action throws an exception. Actions are performed in the order of iteration, if that order is specified. Exceptions thrown by the action are relayed to the caller.

The behavior of an iterator is unspecified if the action modifies the collection in any way (even by calling the remove method or other mutator methods of Iterator subtypes), unless an overriding class has specified a concurrent modification policy.

Subsequent behavior of an iterator is unspecified if the action throws an exception.

Implementation Requirements:

The default implementation behaves as if: 

while (hasNext())
         action.accept(next());
Parameters:
action - The action to be performed for each element
Throws:
NullPointerException - if the specified action is null
Since:
1.8

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https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/Iterator.html