uk.ac.starlink.table

Interface StarTable

All Superinterfaces:

java.lang.AutoCloseable, java.io.Closeable

All Known Implementing Classes:

AbstractStarTable, AsciiStarTable, AsciiTableStarTable, BasePds4StarTable, BeanStarTable, BintableStarTable, CachedParquetStarTable, CalcStarTable, CdfStarTable, ColFitsStarTable, ColumnPermutedStarTable, ColumnStarTable, ColumnStoreStarTable, ConcatStarTable, ConstantStarTable, CsvStarTable, DelimitedPds4StarTable, EcsvStarTable, EmptyStarTable, ExplodedStarTable, FeatherStarTable, GbinStarTable, JDBCStarTable, JoinStarTable, LoopStarTable, MetaCopyStarTable, MetadataStarTable, ParquetStarTable, Pds4StarTable, ProgressBarStarTable, ProgressLineStarTable, RandomResultSetStarTable, RandomStarTable, RowListStarTable, RowPermutedStarTable, RowSubsetStarTable, SelectorStarTable, SequentialParquetStarTable, SequentialResultSetStarTable, StreamStarTable, VOStarTable, WrapperStarTable

public interface StarTable
extends java.io.Closeable

Defines basic table functionality. A table has a fixed number of columns, and a sequence of rows, each of which has one entry for each column. The entry in each column is of the same type (or at least a subtype of a given type) for each row; this type can be determined using the ColumnInfo objects returned by getColumnInfo(int). The first row and the first column are numbered 0.

All StarTables allow sequential access, provided by calling getRowSequence(). This may in general be called multiple times so that more than one iteration can be made through the rows of the table from start to finish. The getRowSplittable() method supports multi-threaded sequential access, and is used by RowRunner. Additionally, if the isRandom() method returns true then the random access methods getRowAccess(), getRow(long) and getCell(long, int) may be used to access table contents directly.

For random tables, the getRow and getCell methods should be thread-safe. Separate RowSequence and RowAccess objects obtained from the same table should be safely usable from different threads, but a given RowSequence/RowAccess in general will not.

In general it is preferred to use getRowAccess() than the equivalent getRow/getCell methods of the table itself, since the assumption of single-threaded use may permit more efficient implementation.

Method Summary

Modifier and Type	Method and Description
void	close() Relinquishes any resources associated with this table.
java.lang.Object	getCell(long irow, int icol) Returns the contents of a given table cell.
java.util.List<ValueInfo>	getColumnAuxDataInfos() Returns an ordered list of ValueInfo objects representing the auxiliary metadata returned by getColumnInfo(int).getAuxData() calls.
int	getColumnCount() Returns the number of columns in this table.
ColumnInfo	getColumnInfo(int icol) Returns the object describing the data in a given column.
java.lang.String	getName() Returns the name of this table, if it has one.
default DescribedValue	getParameterByName(java.lang.String parname) Returns a parameter (table-wide metadata item) of this table located by its name.
java.util.List<DescribedValue>	getParameters() Returns a list of table parameters, that is metadata items which pertain to the entire table.
java.lang.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.
long	getRowCount() Returns the number of rows in this table, if known.
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.
java.net.URL	getURL() Returns the URL of this table, if it has one.
boolean	isRandom() Indicates whether random access is provided by this table.
void	setName(java.lang.String name) Sets the name of this table.
default void	setParameter(DescribedValue dval) Adds the given DescribedValue to the list of parameter metadata objects associated with this table.
void	setURL(java.net.URL url) Sets the URL of this table.

Method Detail

getColumnCount

int getColumnCount()

Returns the number of columns in this table.

Returns:

the number of columns

getRowCount

long getRowCount()

Returns the number of rows in this table, if known. If the number of rows cannot be (easily) determined, a value of -1 will be returned.

Returns:

the number of rows, or -1

getURL

java.net.URL getURL()

Returns the URL of this table, if it has one. A non-null return from this method indicates that this table is in some sense persistent.

Returns:

the URL of this table, or null if none is known

setURL

void setURL(java.net.URL url)

Sets the URL of this table. It ought to be possible in principle to reconstruct this table by reading the resource at url. If called, the supplied url should provide the return value for subsequent calls of getURL().

Parameters:

url - table URL

getName

java.lang.String getName()

Returns the name of this table, if it has one. The meaning of the name is not defined, but it will typically be a short string of text indicating the identity of this table.

Returns:

a name for this table, or null if no suitable one exists

setName

void setName(java.lang.String name)

Sets the name of this table. If called, the supplied name should provide the return value for subsequent calls of getName().

Parameters:

name - table name

getParameters

java.util.List<DescribedValue> getParameters()

Returns a list of table parameters, that is metadata items which pertain to the entire table.

Returns:

a List of DescribedValue objects constituting table-wide metadata not covered elsewhere in this interface

getParameterByName

default DescribedValue getParameterByName(java.lang.String parname)

Returns a parameter (table-wide metadata item) of this table located by its name. If more than one parameter with the given name exists, an arbitrary one will be returned. If no parameter with the given name exists, null will be returned.

Parameters:

parname - the name of the table parameter required

setParameter

default void setParameter(DescribedValue dval)

Adds the given DescribedValue to the list of parameter metadata objects associated with this table. If an item in the parameter list with the same name as the supplied value already exists, it is removed from the list.

Parameters:

dval - the new parameter datum to add

getColumnInfo

ColumnInfo getColumnInfo(int icol)

Returns the object describing the data in a given column.

Parameters:

icol - the column for which header information is required

Returns:

a ValueInfo object for column icol

getColumnAuxDataInfos

java.util.List<ValueInfo> getColumnAuxDataInfos()

Returns an ordered list of ValueInfo objects representing the auxiliary metadata returned by getColumnInfo(int).getAuxData() calls. The idea is that the resulting list can be used to find out the kind of per-column metadata which can be expected to be found in some or all columns of this table. Each item in the returned list should have a unique name, and other characteristics which are applicable to auxData items which may be returned from any of the columns in this table.

The order of the list may indicate some sort of natural ordering of these keys. The returned list is not guaranteed to be complete; it is legal to return an empty list if nothing is known about auxiliary metadata. The list ought not to contain duplicate elements.

Returns:

an unmodifiable ordered set of known metadata keys

See Also:

DefaultValueInfo.getAuxData()

getRowSequence

RowSequence getRowSequence()
                    throws java.io.IOException

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.

Returns:

new RowSequence

Throws:

java.io.IOException - if there is an error providing access

getRowAccess

RowAccess getRowAccess()
                throws java.io.IOException

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.

Returns:

new RowAccess

Throws:

java.io.IOException - if there is an error setting up access

java.lang.UnsupportedOperationException - if isRandom returns false

getRowSplittable

RowSplittable getRowSplittable()
                        throws java.io.IOException

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).

Returns:

new RowSplittable

Throws:

java.io.IOException

See Also:

RowRunner

isRandom

boolean isRandom()

Indicates whether random access is provided by this table. Only if the result is true may the getRowAccess(), getRow(long) and getCell(long, int) methods be used.

Returns:

true if table random access methods are available

getCell

java.lang.Object getCell(long irow,
                         int icol)
                  throws java.io.IOException

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.

Parameters:

irow - the index of the cell's row

icol - the index of the cell's column

Returns:

the contents of this cell

Throws:

java.io.IOException - if there is an error reading the data

java.lang.UnsupportedOperationException - if isRandom returns false

getRow

java.lang.Object[] getRow(long irow)
                   throws java.io.IOException

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.

Parameters:

irow - the index of the row to retrieve

Returns:

an array of the objects in each cell in row irow

Throws:

java.io.IOException - if there is an error reading the data

java.lang.UnsupportedOperationException - if isRandom returns false

close

void close()
    throws java.io.IOException

Relinquishes any resources associated with this table. This may do nothing, and calling it is often not required, but it provides an opportunity to force release of file descriptors or other resources that are not well handled by garbage collection if the table itself holds them. It is not intended for release of heap-based resources, for which garbage collection already provides adequate management.

Following a call to this method, any attempt to use this table or objects such as RowSequences obtained from it will result in undefined behaviour.

Specified by:

close in interface java.lang.AutoCloseable

Specified by:

close in interface java.io.Closeable

Throws:

java.io.IOException