Package org.eclipse.rdf4j.common.iteration

## Class LookAheadIteration<E,​X extends Exception>

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

- All Implemented Interfaces:
    `AutoCloseable`, `CloseableIteration<E,​X>`, `Iteration<E,​X>`
  Direct Known Subclasses:
    `BottomUpJoinIterator`, `CrossProductIteration`, `DescribeIteration`, `DistinctModelReducingUnionIteration`, `FilteringIteration`, `HashJoinIteration`, `IndependentJoingroupBindingsIteration`, `IndependentJoingroupBindingsIteration2`, `IndependentJoingroupBindingsIteration3`, `JoinExecutorBase`, `JoinIterator`, `LeftJoinIterator`, `MemStatementIterator`, `MultiProjectionIterator`, `ParallelExecutorBase`, `ParallelServiceExecutor`, `PathIteration`, `QueueIteration`, `SPARQLCrossProductIteration`, `UnionIteration`, `ZeroLengthPathIteration`

      public abstract class LookAheadIteration<E,​X extends Exception>
      extends AbstractCloseableIteration<E,​X>

  An Iteration that looks one element ahead, if necessary, to handle calls to `hasNext()`. This is a convenient super class for Iterations that have no easy way to tell if there are any more results, but still should implement the java.util.Iteration interface.

- - ### Constructor Summary

    Constructors
    Modifier | Constructor | Description
    --- | --- | ---
    `protected` | `LookAheadIteration()` |

  - ### Method Summary

    All Methods Instance Methods Abstract Methods Concrete Methods
    Modifier and Type | Method | Description
    --- | --- | ---
    `protected abstract E` | `getNextElement()` | Gets the next element.
    `protected void` | `handleClose()` | Called by `AbstractCloseableIteration.close()` when it is called for the first time.
    `boolean` | `hasNext()` | Returns true if the iteration has more elements.
    `E` | `next()` | Returns the next element in the iteration.
    `void` | `remove()` | Throws an `UnsupportedOperationException`.

    - ### 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`

    - ### Methods inherited from interface org.eclipse.rdf4j.common.iteration.Iteration

      `stream`

- - ### Constructor Detail

    - #### LookAheadIteration

          protected LookAheadIteration()

  - ### Method Detail

    - #### getNextElement

          protected abstract E getNextElement()
                                       throws X extends Exception

      Gets the next element. Subclasses should implement this method so that it returns the next element.
      Returns:
        The next element, or null if no more elements are available.
      Throws:
        `X extends Exception`

    - #### hasNext

          public final boolean hasNext()
                                throws X extends Exception

      Description copied from interface: `Iteration`
      Returns true if the iteration has more elements. (In other words, returns true if `Iteration.next()` would return an element rather than throwing a NoSuchElementException.)
      Returns:
        true if the iteration has more elements.
      Throws:
        `X`
        `X extends Exception`

    - #### next

          public final E next()
                       throws X extends Exception

      Description copied from interface: `Iteration`
      Returns the next element in the iteration.
      Returns:
        the next element in the iteration.
      Throws:
        `X extends Exception`

    - #### remove

          public void remove()

      Throws an `UnsupportedOperationException`.

    - #### handleClose

          protected void handleClose()
                              throws X 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 `AbstractCloseableIteration<E,​X extends Exception>`
      Throws:
        `X`
        `X extends Exception`