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package java.util;
import java.util.function.Consumer;
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.
Author: Josh Bloch Type parameters: - <E> – the type of elements returned by this iterator
See Also: API Note: An Enumeration can be converted into an Iterator by using the Enumeration.asIterator method. Since: 1.2
/**
* An iterator over a collection. {@code Iterator} takes the place of
* {@link Enumeration} in the Java Collections Framework. Iterators
* differ from enumerations in two ways:
*
* <ul>
* <li> Iterators allow the caller to remove elements from the
* underlying collection during the iteration with well-defined
* semantics.
* <li> Method names have been improved.
* </ul>
*
* <p>This interface is a member of the
* <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
* Java Collections Framework</a>.
*
* @apiNote
* An {@link Enumeration} can be converted into an {@code Iterator} by
* using the {@link Enumeration#asIterator} method.
*
* @param <E> the type of elements returned by this iterator
*
* @author Josh Bloch
* @see Collection
* @see ListIterator
* @see Iterable
* @since 1.2
*/
public interface Iterator<E> {
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
/**
* Returns {@code true} if the iteration has more elements.
* (In other words, returns {@code true} if {@link #next} would
* return an element rather than throwing an exception.)
*
* @return {@code true} if the iteration has more elements
*/
boolean hasNext();
Returns the next element in the iteration.
Throws: - NoSuchElementException – if the iteration has no more elements
Returns: the next element in the iteration
/**
* Returns the next element in the iteration.
*
* @return the next element in the iteration
* @throws NoSuchElementException if the iteration has no more elements
*/
E next();
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.
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
Implementation Requirements: The default implementation throws an instance of UnsupportedOperationException and performs no other action.
/**
* Removes from the underlying collection the last element returned
* by this iterator (optional operation). This method can be called
* only once per call to {@link #next}.
* <p>
* 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.
* <p>
* The behavior of an iterator is unspecified if this method is called
* after a call to the {@link #forEachRemaining forEachRemaining} method.
*
* @implSpec
* The default implementation throws an instance of
* {@link UnsupportedOperationException} and performs no other action.
*
* @throws UnsupportedOperationException if the {@code remove}
* operation is not supported by this iterator
*
* @throws IllegalStateException if the {@code next} method has not
* yet been called, or the {@code remove} method has already
* been called after the last call to the {@code next}
* method
*/
default void remove() {
throw new UnsupportedOperationException("remove");
}
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.
Params: - action – The action to be performed for each element
Throws: - NullPointerException – if the specified action is null
Implementation Requirements:
The default implementation behaves as if:
while (hasNext())
action.accept(next());
Since: 1.8
/**
* 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.
* <p>
* The behavior of an iterator is unspecified if the action modifies the
* collection in any way (even by calling the {@link #remove remove} method
* or other mutator methods of {@code Iterator} subtypes),
* unless an overriding class has specified a concurrent modification policy.
* <p>
* Subsequent behavior of an iterator is unspecified if the action throws an
* exception.
*
* @implSpec
* <p>The default implementation behaves as if:
* <pre>{@code
* while (hasNext())
* action.accept(next());
* }</pre>
*
* @param action The action to be performed for each element
* @throws NullPointerException if the specified action is null
* @since 1.8
*/
default void forEachRemaining(Consumer<? super E> action) {
Objects.requireNonNull(action);
while (hasNext())
action.accept(next());
}
}