uk.ac.starlink.votable

Class StringElementSizer

java.lang.Object

uk.ac.starlink.votable.StringElementSizer

public abstract class StringElementSizer
extends Object

Object which is able to provide element sizes (string lengths) for table columns containing String[] arrays.

This functionality is required when writing VOTable output; the FIELD headers need to have the common length of the strings, since VOTable output may contain variable-length arrays of fixed-length strings, but not fixed-length arrays of variable-length strings.

A number of implementations are provided. The basic approaches are to read all the elements and find the maximum string length, which in general requires an extra pass through the data, or just provide some sort of guess.

Since:

19 Jun 2025

Author:

Mark Taylor

Field Summary

Fields

Modifier and Type	Field and Description
static StringElementSizer	ASSERT_UNUSED If called upon to provide length values, a false assertion is made.
static StringElementSizer	ERROR_IF_USED If called upon to provide length values, an error will be raised.
static StringElementSizer	FIXED2 A fixed element length of 2 is used.
static StringElementSizer	NOCALC The existing string length values, which may not be legal, are copied.
static StringElementSizer	READ All elements are read and the maximum length used.
static StringElementSizer	SAMPLE The first few elements are read and the maximum length used.

Constructor Summary

Constructors

Constructor and Description
StringElementSizer()

Method Summary

Modifier and Type	Method and Description
abstract int[]	calculateStringArrayElementSizes(StarTable table, int[] icols) Fills in element length values for string array-valued columns in a supplied table.
static StringElementSizer	createFixedSizer(int elSize) Creates an instance that reports a fixed length for all strings.
static StringElementSizer	createSampleReadSizer(int maxRow) Creates an instance which reads some or all of the data to determine the maximum string length.

Methods inherited from class java.lang.Object

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

Field Detail

NOCALC

public static final StringElementSizer NOCALC

The existing string length values, which may not be legal, are copied.

READ

public static final StringElementSizer READ

All elements are read and the maximum length used.

SAMPLE

public static final StringElementSizer SAMPLE

The first few elements are read and the maximum length used.

FIXED2

public static final StringElementSizer FIXED2

A fixed element length of 2 is used.

ERROR_IF_USED

public static final StringElementSizer ERROR_IF_USED

If called upon to provide length values, an error will be raised.

ASSERT_UNUSED

public static final StringElementSizer ASSERT_UNUSED

If called upon to provide length values, a false assertion is made.

Constructor Detail

StringElementSizer

public StringElementSizer()

Method Detail

calculateStringArrayElementSizes

public abstract int[] calculateStringArrayElementSizes(StarTable table,
                                                       int[] icols)
                                                throws IOException

Fills in element length values for string array-valued columns in a supplied table.

The return value is an array the same size as the input icols array whose elements are the calculated string lengths (ValueInfo.getElementSize()) for the corresponding column indices.

Parameters:

table - input table

icols - index array of String[]-valued columns whose element lengths need to be determined

Throws:

IOException

createFixedSizer

public static StringElementSizer createFixedSizer(int elSize)

Creates an instance that reports a fixed length for all strings.

Parameters:

elSize - fixed string length

Returns:

new sizer

createSampleReadSizer

public static StringElementSizer createSampleReadSizer(int maxRow)

Creates an instance which reads some or all of the data to determine the maximum string length.

Parameters:

maxRow - maximum number of rows to read; if not positive, all rows are read

Returns:

new instance