Iterator

AI-generated Key Takeaways

• The Iterator interface provides a way to iterate over a collection of elements, replacing the older Enumeration interface in Java Collections Framework.

• It allows removing elements from the underlying collection during iteration and offers improved method names.

• Iterator includes methods like hasNext(), next(), remove(), and forEachRemaining() to facilitate element traversal and manipulation.

• ListIterator, PrimitiveIterator, and Scanner are some of its known indirect subclasses, each offering specialized functionalities.

public interface Iterator

Known Indirect Subclasses ListIterator<E>, PrimitiveIterator<T, T_CONS>, PrimitiveIterator.OfDouble, PrimitiveIterator.OfInt, PrimitiveIterator.OfLong, Scanner ListIterator<E> An iterator for lists that allows the programmer to traverse the list in either direction, modify the list during iteration, and obtain the iterator's current position in the list.  PrimitiveIterator<T, T_CONS> A base type for primitive specializations of Iterator.  PrimitiveIterator.OfDouble An Iterator specialized for double values.  PrimitiveIterator.OfInt An Iterator specialized for int values.  PrimitiveIterator.OfLong An Iterator specialized for long values.  Scanner A simple text scanner which can parse primitive types and strings using regular expressions.

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.

See Also

• Collection
• ListIterator
• Iterable

Public Method Summary

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.
abstract boolean	hasNext() Returns true if the iteration has more elements.
abstract E	next() Returns the next element in the iteration.
void	remove() Removes from the underlying collection the last element returned by this iterator (optional operation).

Public Methods

public 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.

Parameters

action	The action to be performed for each element

Throws

NullPointerException	if the specified action is null

public abstract 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

public abstract 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

public 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.

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