org.eclipse.rdf4j.common.iteration

## Class QueueIteration<E,T extends Exception>

- java.lang.Object
- - org.eclipse.rdf4j.common.iteration.AbstractCloseableIteration<E,X>
  - - org.eclipse.rdf4j.common.iteration.LookAheadIteration<E,T>
    - - org.eclipse.rdf4j.common.iteration.QueueIteration<E,T>

- All Implemented Interfaces:
    AutoCloseable, CloseableIteration<E,T>, Iteration<E,T>
  Direct Known Subclasses:
    QueueCursor

      public abstract class QueueIteration<E,T extends Exception>
      extends LookAheadIteration<E,T>

  Makes working with a queue easier by adding the methods `done()` and `toss(Exception)` and after converting the Exception to the required type using `convert(Exception)`.
  Author:
    James Leigh

- - ### Constructor Summary

    Constructors
    Modifier | Constructor and Description
    --- | ---
    `protected` | `QueueIteration(BlockingQueue<E> queue)` Creates an `QueueIteration` with the given `BlockingQueue` as its backing queue. It may not be threadsafe to modify or access the given `BlockingQueue` from other locations.
    `protected` | `QueueIteration(int capacity)` Creates an `QueueIteration` with the given (fixed) capacity and default access policy.
    `protected` | `QueueIteration(int capacity, boolean fair)` Creates an `QueueIteration` with the given (fixed) capacity and the specified access policy.

  - ### Method Summary

    All Methods Instance Methods Abstract Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `void` | `checkException()`
    `protected abstract T` | `convert(Exception e)` Converts an exception from the underlying iteration to an exception of type `X`.
    `void` | `done()` Indicates the method `put(Object)` will not be called in the queue anymore.
    `E` | `getNextElement()` Returns the next item in the queue, which may be `null`, or throws an exception.
    `void` | `handleClose()` Called by `AbstractCloseableIteration.close()` when it is called for the first time.
    `void` | `put(E item)` Adds another item to the queue, blocking while the queue is full.
    `void` | `toss(Exception exception)` The next time `LookAheadIteration.next()` is called this exception will be thrown.

    - ### Methods inherited from class org.eclipse.rdf4j.common.iteration.LookAheadIteration

      `hasNext, next, remove`

    - ### Methods inherited from class org.eclipse.rdf4j.common.iteration.AbstractCloseableIteration

      `close, isClosed`

    - ### Methods inherited from class java.lang.Object

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

- - ### Constructor Detail

    - #### QueueIteration

          protected QueueIteration(int capacity)

      Creates an `QueueIteration` with the given (fixed) capacity and default access policy.
      Parameters:
        `capacity` - the capacity of this queue

    - #### QueueIteration

          protected QueueIteration(int capacity,
                                   boolean fair)

      Creates an `QueueIteration` with the given (fixed) capacity and the specified access policy.
      Parameters:
        `capacity` - the capacity of this queue
        `fair` - if `true` then queue accesses for threads blocked on insertion or removal, are processed in FIFO order; if `false` the access order is unspecified.

    - #### QueueIteration

          protected QueueIteration(BlockingQueue<E> queue)

      Creates an `QueueIteration` with the given `BlockingQueue` as its backing queue.
      It may not be threadsafe to modify or access the given `BlockingQueue` from other locations. This method only enables the default `ArrayBlockingQueue` to be overridden.
      Parameters:
        `queue` - A BlockingQueue that is not used in other locations, but will be used as the backing Queue implementation for this cursor.

  - ### Method Detail

    - #### convert

          protected abstract T convert(Exception e)

      Converts an exception from the underlying iteration to an exception of type `X`.

    - #### toss

          public void toss(Exception exception)

      The next time `LookAheadIteration.next()` is called this exception will be thrown. If it is not a QueryEvaluationException or RuntimeException it will be wrapped in a QueryEvaluationException.

    - #### put

          public void put(E item)
                   throws InterruptedException,
                          T extends Exception

      Adds another item to the queue, blocking while the queue is full.
      Throws:
        `InterruptedException`
        `T extends Exception`

    - #### done

          public void done()

      Indicates the method `put(Object)` will not be called in the queue anymore.

    - #### getNextElement

          public E getNextElement()
                           throws T extends Exception

      Returns the next item in the queue, which may be `null`, or throws an exception.
      Specified by:
        `getNextElement` in class `LookAheadIteration<E,T extends Exception>`
      Returns:
        The next element, or `null` if no more elements are available.
      Throws:
        `T extends Exception`

    - #### handleClose

          public void handleClose()
                           throws T extends Exception

      Description copied from class: `AbstractCloseableIteration`
      Called by `AbstractCloseableIteration.close()` when it is called for the first time. This method is only called once on each iteration. By default, this method does nothing.
      Overrides:
        `handleClose` in class `LookAheadIteration<E,T extends Exception>`
      Throws:
        `T extends Exception`

    - #### checkException

          public void checkException()
                              throws T extends Exception

      Throws:
        `T extends Exception`

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