java9.util

Class Iterators

java.lang.Object

java9.util.Iterators

public final class Iterators
extends Object

A place for static default implementations of the new Java 8 default interface methods and static interface methods in the Iterator interface.

Method Summary

Modifier and Type	Method and Description
static <E> Iterator<E>	asIterator(Enumeration<E> en) Returns an Iterator that traverses the remaining elements covered by the passed enumeration.
static <T> Iterator<T>	emptyIterator() Returns an iterator that has no elements.
static <E> void	forEachRemaining(Iterator<E> it, Consumer<? super E> action) Performs the given action for each remaining element until all elements have been processed or the action throws an exception.

Methods inherited from class java.lang.Object

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

Method Detail

forEachRemaining

public static <E> void forEachRemaining(Iterator<E> it,
                                        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. Exceptions thrown by the action are relayed to the caller.

The behavior of an iterator is unspecified if the action modifies the underlying source of elements 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.

The implementation behaves as if:

     while (it.hasNext())
       action.accept(it.next());
 

Type Parameters:

E - the type of the elements for the passed iterator

Parameters:

it - the Iterator whose remaining elements should be processed

action - The action to be performed for each element

Throws:

NullPointerException - if the specified iterator is null

NullPointerException - if the specified action is null

Since:

1.8

asIterator

public static <E> Iterator<E> asIterator(Enumeration<E> en)

Returns an Iterator that traverses the remaining elements covered by the passed enumeration. Traversal is undefined if any methods are called on the passed enumeration after the call to asIterator.

API Note:
This method is intended to help adapt code that produces Enumeration instances to code that consumes Iterator instances. For example, the JarFile.entries() method returns an Enumeration<JarEntry>. This can be turned into an Iterator, and then the forEachRemaining() method can be used:

     JarFile jarFile = ... ;
     Iterators.forEachRemaining(Iterators.asIterator(jarFile.entries()), entry -> ... );
 

Implementation Requirements:
The default implementation returns an Iterator whose hasNext method calls the passed Enumeration's hasMoreElements method, whose next method calls the passed Enumeration's nextElement method, and whose remove method throws UnsupportedOperationException.

Type Parameters:

E - the type of the elements for the passed enumeration

Parameters:

en - the Enumeration whose remaining elements should be processed

Returns:

an Iterator representing the remaining elements of the passed Enumeration

Throws:

NullPointerException - if the specified enumeration is null

Since:

9

emptyIterator

public static <T> Iterator<T> emptyIterator()

Returns an iterator that has no elements. More precisely,

• hasNext always returns false.
• next always throws NoSuchElementException.
• remove always throws IllegalStateException.

Implementations of this method are permitted, but not required, to return the same object from multiple invocations.

Type Parameters:

T - type of elements, if there were any, in the iterator

Returns:

an empty iterator

Since:

1.7