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

Class NullColumn

  • All Implemented Interfaces:
    Column
    public class NullColumn
extends Object
implements Column

    • Constructor Detail

      • NullColumn

        public NullColumn​(ColumnType type,
                  int numRows)

    • Method Detail

      • toAccessor

        @Nonnull
public ColumnAccessor toAccessor()
        Description copied from interface: Column
        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 Column.as(java.lang.Class<? extends T>) which allows for returning null, we define a top-level method that should never return null.
        Specified by:
        toAccessor in interface Column
        Returns:
        a ColumnAccessor representation of the column, this should never return null.

      • as

        @Nullable
public <T> T as​(Class<? extends T> clazz)
        Description copied from interface: Column
        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.
        Specified by:
        as in interface Column
        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.