Iterator (Java SE 9 & JDK 9 ) (original) (raw)

• Type Parameters:
  E - the type of elements returned by this iterator
  All Known Subinterfaces:
  [EventIterator](../../com/sun/jdi/event/EventIterator.html "interface in com.sun.jdi.event"), [ListIterator](../../java/util/ListIterator.html "interface in java.util")<E>, [PrimitiveIterator](../../java/util/PrimitiveIterator.html "interface in java.util")<T,T_CONS>, [PrimitiveIterator.OfDouble](../../java/util/PrimitiveIterator.OfDouble.html "interface in java.util"), [PrimitiveIterator.OfInt](../../java/util/PrimitiveIterator.OfInt.html "interface in java.util"), [PrimitiveIterator.OfLong](../../java/util/PrimitiveIterator.OfLong.html "interface in java.util"), [XMLEventReader](../../javax/xml/stream/XMLEventReader.html "interface in javax.xml.stream")
  All Known Implementing Classes:
  [BeanContextSupport.BCSIterator](../../java/beans/beancontext/BeanContextSupport.BCSIterator.html "class in java.beans.beancontext"), [EventReaderDelegate](../../javax/xml/stream/util/EventReaderDelegate.html "class in javax.xml.stream.util"), [Scanner](../../java/util/Scanner.html "class in java.util")

public interface Iterator
An iterator over a collection. Iterator takes the place ofEnumeration 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

• • Method Summary

  All Methods Instance Methods Abstract Methods Default 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).

• • Method Detail

     * #### hasNext  
     boolean hasNext​()  
     Returns `true` if the iteration has more elements. (In other words, returns `true` if [next()](../../java/util/Iterator.html#next--) would return an element rather than throwing an exception.)  
     Returns:  
     `true` if the iteration has more elements  
     * #### next  
     [E](../../java/util/Iterator.html "type parameter in Iterator") next​()  
     Returns the next element in the iteration.  
     Returns:  
     the next element in the iteration  
     Throws:  
     `[NoSuchElementException](../../java/util/NoSuchElementException.html "class in java.util")` \- 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()](../../java/util/Iterator.html#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](../../java/util/Iterator.html#forEachRemaining-java.util.function.Consumer-) method.  
     Implementation Requirements:  
     The default implementation throws an instance of[UnsupportedOperationException](../../java/lang/UnsupportedOperationException.html "class in java.lang") and performs no other action.  
     Throws:  
     `[UnsupportedOperationException](../../java/lang/UnsupportedOperationException.html "class in java.lang")` \- if the `remove` operation is not supported by this iterator  
     `[IllegalStateException](../../java/lang/IllegalStateException.html "class in java.lang")` \- 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](../../java/util/function/Consumer.html "interface in java.util.function")<? super [E](../../java/util/Iterator.html "type parameter in Iterator")> 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](../../java/util/Iterator.html#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](../../java/lang/NullPointerException.html "class in java.lang")` \- if the specified action is null  
     Since:  
     1.8

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