Stay organized with collections
Save and categorize content based on your preferences.
Iterator
interface Iterator<E : Any!>
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.
Summary
| Public methods |
| open Unit |
Performs the given action for each remaining element until all elements have been processed or the action throws an exception.
|
| abstract Boolean |
Returns true if the iteration has more elements.
|
| abstract E |
Returns the next element in the iteration.
|
| open Unit |
Removes from the underlying collection the last element returned by this iterator (optional operation).
|
Public methods
forEachRemaining
open fun forEachRemaining(action: Consumer<in E>): Unit
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.
| Parameters |
action |
Consumer<in E>: The action to be performed for each element |
| Exceptions |
java.lang.NullPointerException |
if the specified action is null |
hasNext
abstract fun hasNext(): Boolean
Returns true if the iteration has more elements. (In other words, returns true if next would return an element rather than throwing an exception.)
| Return |
Boolean |
true if the iteration has more elements |
next
abstract fun next(): E
Returns the next element in the iteration.
| Return |
E |
the next element in the iteration |
| Exceptions |
java.util.NoSuchElementException |
if the iteration has no more elements |
remove
open fun remove(): Unit
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.
| Exceptions |
java.lang.UnsupportedOperationException |
if the remove operation is not supported by this iterator |
java.lang.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 |
Content and code samples on this page are subject to the licenses described in the Content License. Java and OpenJDK are trademarks or registered trademarks of Oracle and/or its affiliates.
Last updated 2025-02-10 UTC.
[null,null,["Last updated 2025-02-10 UTC."],[],[],null,["# Iterator\n\nAdded in [API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels)\n\nIterator\n========\n\n```\ninterface Iterator\u003cE : Any!\u003e\n```\n\n|-------------------------|\n| [java.util.Iterator](#) |\n\nAn iterator over a collection. `Iterator` takes the place of [Enumeration](/reference/kotlin/java/util/Enumeration) in the Java Collections Framework. Iterators differ from enumerations in two ways:\n\n- Iterators allow the caller to remove elements from the underlying collection during the iteration with well-defined semantics.\n- Method names have been improved.\n\n\u003cbr /\u003e\n\nThis interface is a member of the [Java Collections Framework](https://developer.android.com//reference/java/util/package-summary.html#CollectionsFramework).\n\nSummary\n-------\n\n| Public methods ||\n|---------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|\n| open [Unit](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-unit/index.html) | [forEachRemaining](#forEachRemaining(java.util.function.Consumer))`(`action:` `[Consumer](/reference/kotlin/java/util/function/Consumer)\u003cin` `E\u003e`)` Performs the given action for each remaining element until all elements have been processed or the action throws an exception. |\n| abstract [Boolean](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-boolean/index.html) | [hasNext](#hasNext())`()` Returns `true` if the iteration has more elements. |\n| abstract E | [next](#next())`()` Returns the next element in the iteration. |\n| open [Unit](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-unit/index.html) | [remove](#remove())`()` Removes from the underlying collection the last element returned by this iterator (optional operation). |\n\nPublic methods\n--------------\n\n### forEachRemaining\n\nAdded in [API level 24](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) \n\n```\nopen fun forEachRemaining(action: Consumer\u003cin E\u003e): Unit\n```\n\nPerforms 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.\n\nThe behavior of an iterator is unspecified if the action modifies the collection in any way (even by calling the [remove](#remove()) method or other mutator methods of `Iterator` subtypes), unless an overriding class has specified a concurrent modification policy.\n\nSubsequent behavior of an iterator is unspecified if the action throws an exception.\n\n| Parameters ||\n|----------|----------------------------------------------------------------------------------------------------------------|\n| `action` | [Consumer](/reference/kotlin/java/util/function/Consumer)\\\u003cin E\\\u003e: The action to be performed for each element |\n\n| Exceptions ||\n|----------------------------------|---------------------------------|\n| `java.lang.NullPointerException` | if the specified action is null |\n\n### hasNext\n\nAdded in [API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) \n\n```\nabstract fun hasNext(): Boolean\n```\n\nReturns `true` if the iteration has more elements. (In other words, returns `true` if [next](#next()) would return an element rather than throwing an exception.)\n\n| Return ||\n|------------------------------------------------------------------------------------|-------------------------------------------|\n| [Boolean](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-boolean/index.html) | `true` if the iteration has more elements |\n\n### next\n\nAdded in [API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) \n\n```\nabstract fun next(): E\n```\n\nReturns the next element in the iteration.\n\n| Return ||\n|---|-----------------------------------|\n| E | the next element in the iteration |\n\n| Exceptions ||\n|------------------------------------|---------------------------------------|\n| `java.util.NoSuchElementException` | if the iteration has no more elements |\n\n### remove\n\nAdded in [API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels) \n\n```\nopen fun remove(): Unit\n```\n\nRemoves from the underlying collection the last element returned by this iterator (optional operation). This method can be called only once per call to [next](#next()).\n\nThe 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.\n\nThe behavior of an iterator is unspecified if this method is called after a call to the [forEachRemaining](#forEachRemaining(java.util.function.Consumer)) method.\n\n| Exceptions ||\n|-------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------|\n| `java.lang.UnsupportedOperationException` | if the `remove` operation is not supported by this iterator |\n| `java.lang.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 |"]]
