Package uk.ac.starlink.table

Class EmptyRowSequence

java.lang.Object
uk.ac.starlink.table.EmptyRowSequence
All Implemented Interfaces:
Closeable, AutoCloseable, RowAccess, RowData, RowSequence, RowSplittable, uk.ac.starlink.util.Sequence, uk.ac.starlink.util.Splittable<RowSplittable>
public class EmptyRowSequence extends Object implements RowSplittable, RowAccess
Implementation of both RowSequence and RowAccess which has no rows. Singleton class.
Since:
28 Oct 2004
Author:
Mark Taylor (Starlink)

  • Method Details

    • next

      public boolean next()
      Always returns false.
      Specified by:
      next in interface RowSequence
      Specified by:
      next in interface uk.ac.starlink.util.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 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. After RowSequence.next has returned false, the value is undefined.

      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()
      Specified by:
      split in interface uk.ac.starlink.util.Splittable<RowSplittable>

    • splittableSize

      public long splittableSize()
      Specified by:
      splittableSize in interface uk.ac.starlink.util.Splittable<RowSplittable>

    • getCell

      public 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 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 AutoCloseable
      Specified by:
      close in interface Closeable
      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