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## org.neo4j.helpers.collection
Class IteratorUtil

    java.lang.Object
      org.neo4j.helpers.collection.IteratorUtil

    public abstract class IteratorUtil

extends Object

Contains common functionality regarding `Iterator`s and `Iterable`s.

Constructor Summary
`IteratorUtil()`

Method Summary
`static

`<C extends Collection<T>,T> C`

`
`addToCollection(Iterable<T> iterable, C collection)`
Adds all the items in `iterator` to `collection`.
`static

`<C extends Collection<T>,T> C`

`
`addToCollection(Iterator<T> iterator, C collection)`
Adds all the items in `iterator` to `collection`.
`static

`<T> Collection<T>`

`
`asCollection(Iterable<T> iterable)`
Creates a collection from an iterable.
`static ClosableIterable<String>` | `asIterable(File file)` Creates an `Iterable` for iterating over the lines of a text file.
`static

`<T> Iterable<T>`

`
`asIterable(Iterator<T> iterator)`
Exposes `iterator` as an `Iterable`.
`static ClosableIterator<String>` | `asIterator(File file)` Creates an `Iterator` for iterating over the lines of a text file.
`static

`<T> int`

`
`count(Iterable<T> iterable)`
Counts the number of items in the `iterable` by looping through it.
`static

`<T> int`

`
`count(Iterator<T> iterator)`
Counts the number of items in the `iterator` by looping through it.
`static

`<T> T`

`
`first(Iterable<T> iterable)`
Returns the given iterable's first element.
`static

`<T> T`

`
`first(Iterator<T> iterator)`
Returns the given iterator's first element.
`static

`<T> T`

`
`firstOrNull(Iterable<T> iterable)`
Returns the given iterable's first element or `null` if no element found.
`static

`<T> T`

`
`firstOrNull(Iterator<T> iterator)`
Returns the given iterator's first element or `null` if no element found.
`static

`<T> T`

`
`fromEnd(Iterable<T> iterable, int n)`
Returns the iterator's n:th item from the end of the iteration.
`static

`<T> T`

`
`fromEnd(Iterator<T> iterator, int n)`
Returns the iterator's n:th item from the end of the iteration.
`static

`<T> T`

`
`fromEndOrNull(Iterable<T> iterable, int countFromEnd)`
Returns the iterator's n:th item from the end of the iteration.
`static

`<T> T`

`
`fromEndOrNull(Iterator<T> iterator, int n)`
Returns the iterator's n:th item from the end of the iteration.
`static

`<T> T`

`
`last(Iterable<T> iterable)`
Returns the given iterable's last element.
`static

`<T> T`

`
`last(Iterator<T> iterator)`
Returns the given iterator's last element.
`static

`<T> T`

`
`lastOrNull(Iterable<T> iterable)`
Returns the given iterable's last element or `null` if no element found.
`static

`<T> T`

`
`lastOrNull(Iterator<T> iterator)`
Returns the given iterator's last element or `null` if no element found.
`static

`<T> Iterable<T>`

`
`loop(Iterator<T> iterator)`
Convenience method for looping over an `Iterator`.
`static

`<T> T`

`
`single(Iterable<T> iterable)`
Returns the given iterable's single element.
`static

`<T> T`

`
`single(Iterator<T> iterator)`
Returns the given iterator's single element.
`static

`<T> T`

`
`singleOrNull(Iterable<T> iterable)`
Returns the given iterable's single element or `null` if no element found.
`static

`<T> T`

`
`singleOrNull(Iterator<T> iterator)`
Returns the given iterator's single element or `null` if no element found.
`static

`<T> void`

`
`streamToFile(Iterable<T> iterable, File file)`
`static

`<T> void`

`
`streamToFile(Iterator<T> iterator, File file)`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

### IteratorUtil

    public IteratorUtil()

Method Detail

### firstOrNull

    public static <T> T firstOrNull(Iterator<T> iterator)

  Returns the given iterator's first element or `null` if no element found.

  Type Parameters:
    `T` - the type of elements in `iterator`.
  Parameters:
    `iterator` - the `Iterator` to get elements from.
  Returns:
    the first element in the `iterator`, or `null` if no element found.

### first

    public static <T> T first(Iterator<T> iterator)

  Returns the given iterator's first element. If no element is found a `NoSuchElementException` is thrown.

  Type Parameters:
    `T` - the type of elements in `iterator`.
  Parameters:
    `iterator` - the `Iterator` to get elements from.
  Returns:
    the first element in the `iterator`.
  Throws:
    `{@link` - NoSuchElementException} if no element found.

### lastOrNull

    public static <T> T lastOrNull(Iterator<T> iterator)

  Returns the given iterator's last element or `null` if no element found.

  Type Parameters:
    `T` - the type of elements in `iterator`.
  Parameters:
    `iterator` - the `Iterator` to get elements from.
  Returns:
    the last element in the `iterator`, or `null` if no element found.

### last

    public static <T> T last(Iterator<T> iterator)

  Returns the given iterator's last element. If no element is found a `NoSuchElementException` is thrown.

  Type Parameters:
    `T` - the type of elements in `iterator`.
  Parameters:
    `iterator` - the `Iterator` to get elements from.
  Returns:
    the last element in the `iterator`.
  Throws:
    `{@link` - NoSuchElementException} if no element found.

### singleOrNull

    public static <T> T singleOrNull(Iterator<T> iterator)

  Returns the given iterator's single element or `null` if no element found. If there is more than one element in the iterator a `NoSuchElementException` will be thrown.

  Type Parameters:
    `T` - the type of elements in `iterator`.
  Parameters:
    `iterator` - the `Iterator` to get elements from.
  Returns:
    the single element in `iterator`, or `null` if no element found.
  Throws:
    `{@link` - NoSuchElementException} if more than one element was found.

### single

    public static <T> T single(Iterator<T> iterator)

  Returns the given iterator's single element. If there are no elements or more than one element in the iterator a `NoSuchElementException` will be thrown.

  Type Parameters:
    `T` - the type of elements in `iterator`.
  Parameters:
    `iterator` - the `Iterator` to get elements from.
  Returns:
    the single element in the `iterator`.
  Throws:
    `{@link` - NoSuchElementException} if there isn't exactly one element.

### fromEnd

    public static <T> T fromEnd(Iterator<T> iterator,
                                int n)

  Returns the iterator's n:th item from the end of the iteration. If the iterator has got less than n-1 items in it `NoSuchElementException` is thrown.

  Type Parameters:
    `T` - the type of elements in `iterator`.
  Parameters:
    `iterator` - the `Iterator` to get elements from.
    `n` - the n:th item from the end to get.
  Returns:
    the iterator's n:th item from the end of the iteration.
  Throws:
    `NoSuchElementException` - if the iterator contains less than n-1 items.

### fromEndOrNull

    public static <T> T fromEndOrNull(Iterator<T> iterator,
                                      int n)

  Returns the iterator's n:th item from the end of the iteration. If the iterator has got less than n-1 items in it `null` is returned.

  Type Parameters:
    `T` - the type of elements in `iterator`.
  Parameters:
    `iterator` - the `Iterator` to get elements from.
    `n` - the n:th item from the end to get.
  Returns:
    the iterator's n:th item from the end of the iteration, or `null` if the iterator doesn't contain that many items.

### firstOrNull

    public static <T> T firstOrNull(Iterable<T> iterable)

  Returns the given iterable's first element or `null` if no element found.

  Type Parameters:
    `T` - the type of elements in `iterable`.
  Parameters:
    `iterable` - the `Iterable` to get elements from.
  Returns:
    the first element in the `iterable`, or `null` if no element found.

### first

    public static <T> T first(Iterable<T> iterable)

  Returns the given iterable's first element. If no element is found a `NoSuchElementException` is thrown.

  Type Parameters:
    `T` - the type of elements in `iterable`.
  Parameters:
    `iterable` - the `Iterable` to get elements from.
  Returns:
    the first element in the `iterable`.
  Throws:
    `{@link` - NoSuchElementException} if no element found.

### lastOrNull

    public static <T> T lastOrNull(Iterable<T> iterable)

  Returns the given iterable's last element or `null` if no element found.

  Type Parameters:
    `T` - the type of elements in `iterable`.
  Parameters:
    `iterable` - the `Iterable` to get elements from.
  Returns:
    the last element in the `iterable`, or `null` if no element found.

### last

    public static <T> T last(Iterable<T> iterable)

  Returns the given iterable's last element. If no element is found a `NoSuchElementException` is thrown.

  Type Parameters:
    `T` - the type of elements in `iterable`.
  Parameters:
    `iterable` - the `Iterable` to get elements from.
  Returns:
    the last element in the `iterable`.
  Throws:
    `{@link` - NoSuchElementException} if no element found.

### singleOrNull

    public static <T> T singleOrNull(Iterable<T> iterable)

  Returns the given iterable's single element or `null` if no element found. If there is more than one element in the iterable a `NoSuchElementException` will be thrown.

  Type Parameters:
    `T` - the type of elements in `iterable`.
  Parameters:
    `iterable` - the `Iterable` to get elements from.
  Returns:
    the single element in `iterable`, or `null` if no element found.
  Throws:
    `{@link` - NoSuchElementException} if more than one element was found.

### single

    public static <T> T single(Iterable<T> iterable)

  Returns the given iterable's single element. If there are no elements or more than one element in the iterable a `NoSuchElementException` will be thrown.

  Type Parameters:
    `T` - the type of elements in `iterable`.
  Parameters:
    `iterable` - the `Iterable` to get elements from.
  Returns:
    the single element in the `iterable`.
  Throws:
    `{@link` - NoSuchElementException} if there isn't exactly one element.

### fromEndOrNull

    public static <T> T fromEndOrNull(Iterable<T> iterable,
                                      int countFromEnd)

  Returns the iterator's n:th item from the end of the iteration. If the iterator has got less than n-1 items in it `null` is returned.

  Type Parameters:
    `T` - the type of elements in `iterator`.
  Parameters:
    `iterable` - the `Iterable` to get elements from.
    `countFromEnd` - the n:th item from the end to get.
  Returns:
    the iterator's n:th item from the end of the iteration, or `null` if the iterator doesn't contain that many items.

### fromEnd

    public static <T> T fromEnd(Iterable<T> iterable,
                                int n)

  Returns the iterator's n:th item from the end of the iteration. If the iterator has got less than n-1 items in it `NoSuchElementException` is thrown.

  Type Parameters:
    `T` - the type of elements in `iterator`.
  Parameters:
    `iterable` - the `Iterable` to get elements from.
    `n` - the n:th item from the end to get.
  Returns:
    the iterator's n:th item from the end of the iteration.
  Throws:
    `NoSuchElementException` - if the iterator contains less than n-1 items.

### addToCollection

    public static <C extends Collection<T>,T> C addToCollection(Iterator<T> iterator,
                                                                C collection)

  Adds all the items in `iterator` to `collection`.

  Type Parameters:
    `C` - the type of `Collection` to add to items to.
    `T` - the type of items in the collection and iterator.
  Parameters:
    `iterator` - the `Iterator` to grab the items from.
    `collection` - the `Collection` to add the items to.
  Returns:
    the `collection` which was passed in, now filled with the items from `iterator`.

### addToCollection

    public static <C extends Collection<T>,T> C addToCollection(Iterable<T> iterable,
                                                                C collection)

  Adds all the items in `iterator` to `collection`.

  Type Parameters:
    `C` - the type of `Collection` to add to items to.
    `T` - the type of items in the collection and iterator.
  Parameters:
    `iterable` - the `Iterator` to grab the items from.
    `collection` - the `Collection` to add the items to.
  Returns:
    the `collection` which was passed in, now filled with the items from `iterator`.

### loop

    public static <T> Iterable<T> loop(Iterator<T> iterator)

  Convenience method for looping over an `Iterator`. Converts the `Iterator` to an `Iterable` by wrapping it in an `Iterable` that returns the `Iterator`. It breaks the contract of `Iterable` in that it returns the supplied iterator instance for each call to `iterator()` on the returned `Iterable` instance. This method exists to make it easy to use an `Iterator` in a for-loop.

  Type Parameters:
    `T` - the type of items in the iterator.
  Parameters:
    `iterator` - the iterator to expose as an `Iterable`.
  Returns:
    the supplied iterator posing as an `Iterable`.

### asIterable

    public static <T> Iterable<T> asIterable(Iterator<T> iterator)

  Exposes `iterator` as an `Iterable`. It breaks the contract of `Iterable` in that it returns the supplied iterator instance for each call to `iterator()` on the returned `Iterable` instance. This method mostly exists to make it easy to use an `Iterator` in a for-loop.

  Type Parameters:
    `T` - the type of items in the iterator.
  Parameters:
    `iterator` - the iterator to expose as an `Iterable`.
  Returns:
    the supplied iterator posing as an `Iterable`.

### count

    public static <T> int count(Iterator<T> iterator)

  Counts the number of items in the `iterator` by looping through it.

  Type Parameters:
    `T` - the type of items in the iterator.
  Parameters:
    `iterator` - the `Iterator` to count items in.
  Returns:
    the number of found in `iterator`.

### count

    public static <T> int count(Iterable<T> iterable)

  Counts the number of items in the `iterable` by looping through it.

  Type Parameters:
    `T` - the type of items in the iterator.
  Parameters:
    `iterable` - the `Iterable` to count items in.
  Returns:
    the number of found in `iterator`.

### asCollection

    public static <T> Collection<T> asCollection(Iterable<T> iterable)

  Creates a collection from an iterable.

  Type Parameters:
    `T` - The generic type of both the iterable and the collection.
  Parameters:
    `iterable` - The iterable to create the collection from.
  Returns:
    a collection containing all items from the iterable.

### asIterable

    public static ClosableIterable<String> asIterable(File file)

  Creates an `Iterable` for iterating over the lines of a text file.

  Parameters:
    `file` - the file to get the lines for.
  Returns:
    an `Iterable` for iterating over the lines of a text file.

### asIterator

    public static ClosableIterator<String> asIterator(File file)
                                               throws IOException

  Creates an `Iterator` for iterating over the lines of a text file. The opened file is closed if an exception occurs during reading or when the files has been read through all the way.

  Parameters:
    `file` - the file to get the lines for.
  Returns:
    an `Iterator` for iterating over the lines of a text file.
  Throws:
    `IOException`

### streamToFile

    public static <T> void streamToFile(Iterable<T> iterable,
                                        File file)
                             throws IOException

  Throws:
    `IOException`

### streamToFile

    public static <T> void streamToFile(Iterator<T> iterator,
                                        File file)
                             throws IOException

  Throws:
    `IOException`

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