Package org.apache.druid.query.rowsandcols.column

Interface Column

All Known Implementing Classes:
ColumnAccessorBasedColumn, ColumnHolderRACColumn, ConstantObjectColumn, DoubleArrayColumn, IntArrayColumn, LimitedColumn, LongArrayColumn, NullColumn, ObjectArrayColumn
public interface Column
An interface representing a Column of data. This interface prescribes that a ColumnAccessor must be defined on the column, but also offers an as(java.lang.Class<? extends T>) method to allow for optimized specific implementations of semantically meaningful logic. That is, the expectation is that some things work with Column objects might choose to first ask the Column object to become some other interface. If the Column knows how to do a good job as the requested interface, it can return its own concrete implementation of the interface and run the necessary logic in its own optimized fashion. If the Column instance does not know how to implement the semantic interface, it is expected that the ColumnAccessor will be leveraged to implement whatever logic is required.

  • Method Summary

    Modifier and Type
    Method
    Description
    <T> T
    as(Class<? extends T> clazz)
    Asks the Column to return itself as a concrete implementation of a specific interface.
    ColumnAccessor
    toAccessor()
    Returns the column as a ColumnAccessor.

  • Method Details

    • toAccessor

      @Nonnull ColumnAccessor toAccessor()
      Returns the column as a ColumnAccessor. Semantically, this would be equivalent to calling Column.as(ColumnAccessor.class). However, being able to implement this interface is part of the explicit contract of implementing this interface, so instead of relying on as(java.lang.Class<? extends T>) which allows for returning null, we define a top-level method that should never return null.
      Returns:
      a ColumnAccessor representation of the column, this should never return null.

    • as

      @Nullable <T> T as(Class<? extends T> clazz)
      Asks the Column to return itself as a concrete implementation of a specific interface. The interface asked for will tend to be a semantically-meaningful interface. This method allows the calling code to interrogate the Column object about whether it can offer a meaningful optimization of the semantic interface. If a Column cannot do anything specifically optimal for the interface requested, it should return null instead of trying to come up with its own default implementation.
      Type Parameters:
      T - The interface that the calling code wants a concrete implementation of
      Parameters:
      clazz - A class object representing the interface that the calling code wants a concrete implementation of
      Returns:
      A concrete implementation of the interface, or null if there is no meaningful optimization to be had through a local implementation of the interface.