uk.ac.starlink.ttools.jel

Class JELTable

java.lang.Object

uk.ac.starlink.table.WrapperStarTable

uk.ac.starlink.ttools.jel.JELTable

All Implemented Interfaces:

Closeable, AutoCloseable, StarTable

public class JELTable
extends WrapperStarTable

Wrapper table which is constructed entirely of columns defined by JEL expressions based on the base table.

Since:

1 Sep 2005

Author:

Mark Taylor

Field Summary

Fields inherited from class uk.ac.starlink.table.WrapperStarTable

baseTable

Constructor Summary

Constructors

Constructor and Description
JELTable(StarTable baseTable, ColumnInfo[] colInfos, String[] exprs) Constructor.

Method Summary

Modifier and Type	Method and Description
static StarTable	createJELTable(StarTable baseTable, String[] exprs) Creates a JELTable from a base table and a list of column expressions.
static StarTable	createJELTable(StarTable baseTable, ValueInfo[] infos, String[] exprs) Convenience factory method.
Object	getCell(long irow, int icol) Returns the contents of a given table cell.
int	getColumnCount() Returns the number of columns in this table.
ColumnInfo	getColumnInfo(int icol) Returns the object describing the data in a given column.
Object[]	getRow(long irow) Returns the contents of a given table row.
RowAccess	getRowAccess() Returns an object which can provide random access to this table's data, if random access is implemented.
RowSequence	getRowSequence() Returns an object which can iterate over all the rows in the table sequentially.
RowSplittable	getRowSplittable() Returns an object which can iterate over all the rows in the table, but which may also be requested to split recursively for potentially parallel processing.

Methods inherited from class uk.ac.starlink.table.WrapperStarTable

checkedLongToInt, close, getBaseTable, getColumnAuxDataInfos, getName, getParameterByName, getParameters, getRowCount, getURL, isRandom, setName, setParameter, setURL, toString

Methods inherited from class java.lang.Object

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

Constructor Detail

JELTable

public JELTable(StarTable baseTable,
                ColumnInfo[] colInfos,
                String[] exprs)
         throws gnu.jel.CompilationException

Constructor. The number of columns is the same as the number of elements of colInfos, which must be the same as the number of elements in exprs. If the contentClass attributes of the colInfos elements are non-null, they must be compatible with the actual types of the evaluated expressions. If they are not, an IllegalArgumentException will be thrown.

Parameters:

baseTable - table which provides both behaviour determining whether random access is available etc, and an evaluation context for the JEL calculations

colInfos - column metadata for each of the columns in this table

exprs - JEL expressions, evaluated in a context determined by baseTable, which give the data for this table.

Throws:

gnu.jel.CompilationException

Method Detail

getColumnCount

public int getColumnCount()

Description copied from interface: StarTable

Returns the number of columns in this table.

Specified by:

getColumnCount in interface StarTable

Overrides:

getColumnCount in class WrapperStarTable

Returns:

the number of columns

getColumnInfo

public ColumnInfo getColumnInfo(int icol)

Description copied from interface: StarTable

Returns the object describing the data in a given column.

Specified by:

getColumnInfo in interface StarTable

Overrides:

getColumnInfo in class WrapperStarTable

Parameters:

icol - the column for which header information is required

Returns:

a ValueInfo object for column icol

getCell

public Object getCell(long irow,
                      int icol)
               throws IOException

Description copied from interface: StarTable

Returns the contents of a given table cell. The class of the returned object should be the same as, or a subclass of, the class returned by getColumnInfo(icol).getContentClass().

This method is safe for concurrent use from multiple threads, but in general it is recommended to use a RowAccess instead.

Specified by:

getCell in interface StarTable

Overrides:

getCell in class WrapperStarTable

Parameters:

irow - the index of the cell's row

icol - the index of the cell's column

Returns:

the contents of this cell

Throws:

IOException - if there is an error reading the data

getRow

public Object[] getRow(long irow)
                throws IOException

Description copied from interface: StarTable

Returns the contents of a given table row. The returned value is equivalent to an array formed of all the objects returned by getCell(irow,icol) for all the columns icol in sequence.

This method is safe for concurrent use from multiple threads, but in general it is recommended to use a RowAccess instead.

Specified by:

getRow in interface StarTable

Overrides:

getRow in class WrapperStarTable

Parameters:

irow - the index of the row to retrieve

Returns:

an array of the objects in each cell in row irow

Throws:

IOException - if there is an error reading the data

getRowSequence

public RowSequence getRowSequence()
                           throws IOException

Description copied from interface: StarTable

Returns an object which can iterate over all the rows in the table sequentially. Each such returned object is safe for use within a single thread, but not in general from multiple threads concurrently.

Specified by:

getRowSequence in interface StarTable

Overrides:

getRowSequence in class WrapperStarTable

Returns:

new RowSequence

Throws:

IOException - if there is an error providing access

getRowAccess

public RowAccess getRowAccess()
                       throws IOException

Description copied from interface: StarTable

Returns an object which can provide random access to this table's data, if random access is implemented. Each such returned object is safe for use within a single thread, but not in general from multiple threads concurrently.

Specified by:

getRowAccess in interface StarTable

Overrides:

getRowAccess in class WrapperStarTable

Returns:

new RowAccess

Throws:

IOException - if there is an error setting up access

getRowSplittable

public RowSplittable getRowSplittable()
                               throws IOException

Description copied from interface: StarTable

Returns an object which can iterate over all the rows in the table, but which may also be requested to split recursively for potentially parallel processing.

The return value must be non-null, and may provide splitting arrangements specially appropriate for the implementation. If this table 'wraps' an upstream table, it is usually best to base the implementation on calls to the the upstream getRowSplittable method, so that upstream policy about how to divide up the table is respected. However, implementations without special requirements may return Tables.getDefaultRowSplittable(this).

Specified by:

getRowSplittable in interface StarTable

Overrides:

getRowSplittable in class WrapperStarTable

Returns:

new RowSplittable

Throws:

IOException

See Also:

RowRunner

createJELTable

public static StarTable createJELTable(StarTable baseTable,
                                       ValueInfo[] infos,
                                       String[] exprs)
                                throws ExecutionException

Convenience factory method. It turns all the supplied infos into ColumnInfos and rethrows any CompilationException as an ExecutionException.

Parameters:

baseTable - table which provides both behaviour determining whether random access is available etc, and an evaluation context for the JEL calculations

infos - metadata used to construct column metadata

exprs - JEL expressions, evaluated in a context determined by baseTable, which give the data for this table

Returns:

new table

Throws:

ExecutionException

createJELTable

public static StarTable createJELTable(StarTable baseTable,
                                       String[] exprs)
                                throws gnu.jel.CompilationException

Creates a JELTable from a base table and a list of column expressions. If the expressions can be determined to correspond to columns from the base table, the metadata is propagated. Otherwise, column names are constructed from the expression strings.

Parameters:

baseTable - table which provides both behaviour determining whether random access is available etc, and an evaluation context for the JEL calculations

exprs - JEL expressions, evaluated in a context determined by baseTable, which give the data for this table

Returns:

new table

Throws:

gnu.jel.CompilationException