Package org.apache.calcite.linq4j

Class MemoryEnumerator<E>

java.lang.Object
org.apache.calcite.linq4j.MemoryEnumerator<E>
Type Parameters:
E - Row value
All Implemented Interfaces:
AutoCloseable, Enumerator<MemoryFactory.Memory<E>>
public class MemoryEnumerator<@Nullable E> extends Object implements Enumerator<MemoryFactory.Memory<E>>
Enumerator that keeps some recent and some "future" values.

  • Method Details

    • current

      public MemoryFactory.Memory<E> current()
      Description copied from interface: Enumerator
      Gets the current element in the collection.

      After an enumerator is created or after the Enumerator.reset() method is called, the Enumerator.moveNext() method must be called to advance the enumerator to the first element of the collection before reading the value of the current property; otherwise, current is undefined.

      This method also throws NoSuchElementException if the last call to moveNext returned false, which indicates the end of the collection.

      This method does not move the position of the enumerator, and consecutive calls to current return the same object until either moveNext or reset is called.

      An enumerator remains valid as long as the collection remains unchanged. If changes are made to the collection, such as adding, modifying, or deleting elements, the enumerator is irrecoverably invalidated. The next call to moveNext or reset may, at the discretion of the implementation, throw a ConcurrentModificationException. If the collection is modified between moveNext and current, current returns the element that it is set to, even if the enumerator is already invalidated.

      Specified by:
      current in interface Enumerator<E>
      Returns:
      Current element

    • moveNext

      public boolean moveNext()
      Description copied from interface: Enumerator
      Advances the enumerator to the next element of the collection.

      After an enumerator is created or after the reset method is called, an enumerator is positioned before the first element of the collection, and the first call to the moveNext method moves the enumerator over the first element of the collection.

      If moveNext passes the end of the collection, the enumerator is positioned after the last element in the collection and moveNext returns false. When the enumerator is at this position, subsequent calls to moveNext also return false until #reset is called.

      An enumerator remains valid as long as the collection remains unchanged. If changes are made to the collection, such as adding, modifying, or deleting elements, the enumerator is irrecoverably invalidated. The next call to moveNext or Enumerator.reset() may, at the discretion of the implementation, throw a ConcurrentModificationException.

      Specified by:
      moveNext in interface Enumerator<E>
      Returns:
      true if the enumerator was successfully advanced to the next element; false if the enumerator has passed the end of the collection

    • reset

      public void reset()
      Description copied from interface: Enumerator
      Sets the enumerator to its initial position, which is before the first element in the collection.

      An enumerator remains valid as long as the collection remains unchanged. If changes are made to the collection, such as adding, modifying, or deleting elements, the enumerator is irrecoverably invalidated. The next call to Enumerator.moveNext() or reset may, at the discretion of the implementation, throw a ConcurrentModificationException.

      This method is optional; it may throw UnsupportedOperationException.

      Notes to Implementers

      All calls to Reset must result in the same state for the enumerator. The preferred implementation is to move the enumerator to the beginning of the collection, before the first element. This invalidates the enumerator if the collection has been modified since the enumerator was created, which is consistent with Enumerator.moveNext() and Enumerator.current().

      Specified by:
      reset in interface Enumerator<E>

    • close

      public void close()
      Description copied from interface: Enumerator
      Closes this enumerable and releases resources.

      This method is idempotent. Calling it multiple times has the same effect as calling it once.

      Specified by:
      close in interface AutoCloseable
      Specified by:
      close in interface Enumerator<E>