uk.ac.starlink.table

## Class EmptyRowSequence

- java.lang.Object
- - uk.ac.starlink.table.EmptyRowSequence

- All Implemented Interfaces:
    java.io.Closeable, java.lang.AutoCloseable, RowAccess, RowData, RowSequence, RowSplittable, Sequence, Splittable<RowSplittable>

      public class EmptyRowSequence
      extends java.lang.Object
      implements RowSplittable, RowAccess

  Implementation of both RowSequence and RowAccess which has no rows. Singleton class.
  Since:
    28 Oct 2004

- - ### Method Summary

    All Methods Static Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `void` | `close()` Does nothing.
    `java.lang.Object` | `getCell(int icol)` Always throws IllegalStateException.
    `static EmptyRowSequence` | `getInstance()` Returns singleton instance of this class.
    `java.lang.Object[]` | `getRow()` Always throws IllegalStateException.
    `boolean` | `next()` Always returns false.
    `java.util.function.LongSupplier` | `rowIndex()` Returns a supplier for the index of the row currently being processed, if possible.
    `void` | `setRowIndex(long irow)` Sets the row index to which subsequent data accesses will refer.
    `RowSplittable` | `split()` Attempts to partition this object into two halves, ideally of similar size.
    `long` | `splittableSize()` Provides an estimate of the number of processable items in this object.

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

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

- - ### Method Detail

    - #### next

          public boolean next()

      Always returns false.
      Specified by:
        `next` in interface `RowSequence`
      Specified by:
        `next` in interface `Sequence`
      Returns:
        `true` iff this sequence has been advanced to the next row

    - #### setRowIndex

          public void setRowIndex(long irow)

      Description copied from interface: `RowAccess`
      Sets the row index to which subsequent data accesses will refer.

      This method must be called before the first invocation of `RowAccess.getCell(int)`/`RowAccess.getRow()`, otherwise behaviour is undefined (but implementations will likely throw an unchecked exception on subsequent getCell/getRow calls). The effect of setting the value to an out of range value is undefined; it may throw an exception here, or during subsequent calls, or behave otherwise.

      Specified by:
        `setRowIndex` in interface `RowAccess`
      Parameters:
        `irow` - row index

    - #### rowIndex

          public java.util.function.LongSupplier rowIndex()

      Description copied from interface: `RowSplittable`
      Returns a supplier for the index of the row currently being processed, if possible. The row index is a global value; when accessing the first row of a top-level RowSplittable, the value returned by this supplier should be the first index in the table. But for objects resulting from splitting a top-level instance into sub-instances, the return value should reflect the index in the original sequence of rows; each index should be returned from only one of the splittables resulting from splitting a top-level instance.

      Typically, the row index will start at 0 and increment for each row, but the numbering may be different depending on the requirements of the implementation or usage.

      Before the `RowSequence.next()` method has been called, the return value will be one less than the first row index.

      Depending on the implementation, it may not be possible to determine the row index (for instance if the sequence is split into sub-splittables of unknown size). In such cases, this method returns null. The null-ness of the return value must be the same for all instances of the splittable hierarchy for a given sequence, so don't return a non-null value for the first splittable and then null values for some or all of its children.

      Specified by:
        `rowIndex` in interface `RowSplittable`
      Returns:
        supplier for the globally-referenced row index value of the current row of this sequence, or null

    - #### split

          public RowSplittable split()

      Description copied from interface: `Splittable`
      Attempts to partition this object into two halves, ideally of similar size. If a non-null value is returned, then the content previously contained by this object is now split between this object and the returned object. If for any reason a split is not carried out, null is returned.

      Following a successful call, the two parts may be processed in different threads.

      Specified by:
        `split` in interface `Splittable<RowSplittable>`
      Returns:
        other half of this splittable, or null
      See Also:
        `Spliterator.trySplit()`

    - #### splittableSize

          public long splittableSize()

      Description copied from interface: `Splittable`
      Provides an estimate of the number of processable items in this object. A processable item is not a well-defined quantity, but it should generally be something that can be processed fast. For instance, if this object represents a collection of collections, the value that should be returned is the total number of elements rather than the number of collections.

      If no estimate for the size is available, a negative value should be returned.

      Specified by:
        `splittableSize` in interface `Splittable<RowSplittable>`
      Returns:
        approximate size, or negative value if not known

    - #### getCell

          public java.lang.Object getCell(int icol)

      Always throws IllegalStateException.
      Specified by:
        `getCell` in interface `RowAccess`
      Specified by:
        `getCell` in interface `RowData`
      Specified by:
        `getCell` in interface `RowSequence`
      Parameters:
        `icol` - column index
      Returns:
        the contents of cell `icol` in the current row

    - #### getRow

          public java.lang.Object[] getRow()

      Always throws IllegalStateException.
      Specified by:
        `getRow` in interface `RowAccess`
      Specified by:
        `getRow` in interface `RowData`
      Specified by:
        `getRow` in interface `RowSequence`
      Returns:
        an array of the objects in each cell in row `irow`

    - #### close

          public void close()

      Does nothing.
      Specified by:
        `close` in interface `java.io.Closeable`
      Specified by:
        `close` in interface `java.lang.AutoCloseable`
      Specified by:
        `close` in interface `RowAccess`
      Specified by:
        `close` in interface `RowSequence`

    - #### getInstance

          public static EmptyRowSequence getInstance()

      Returns singleton instance of this class.
      Returns:
        instance