Interface ValueInfo

  • All Known Implementing Classes:
    ColumnInfo, DefaultValueInfo, URLValueInfo

    public interface ValueInfo
    Describes a value, for instance one obtained from cells in a given table column, or from a table parameter. This interface encapsulates the name, description, UCD etc, as well as information about the kind of object that the value can assume, such as Java class and array shape where applicable. It will normally be associated with a method which is declared to return one or more Objects; use of the information in this class can then be used to make additional sense of the object(s) thus returned.
    Author:
    Mark Taylor (Starlink)
    • Method Summary

      All Methods Instance Methods Abstract Methods 
      Modifier and Type Method Description
      java.lang.String formatValue​(java.lang.Object value, int maxLength)
      Returns a string representation of a given value described by this ValueInfo.
      java.lang.Class getContentClass()
      Returns the java class of the values described by this object.
      java.lang.String getDescription()
      Returns a description of the values described by this object.
      DomainMapper[] getDomainMappers()
      Returns an array of objects which may be able to convert from the values described by this info to a particular target value domain.
      int getElementSize()
      May indicate the size of a value element stored as the value of this info.
      java.lang.String getName()
      Returns the name of this object.
      int[] getShape()
      Returns the shape associated with array value types.
      java.lang.String getUCD()
      Returns the Unified Column Descriptor string applying to the values described by this object.
      java.lang.String getUnitString()
      Returns a string representing the units of the values described by this object.
      java.lang.String getUtype()
      Returns the Utype string applying to the values described by this object.
      boolean isArray()
      Indicates whether the values described by this object are java arrays.
      boolean isNullable()
      Indicates whether values returned described by this object may have the value null.
      java.lang.Object unformatString​(java.lang.String rep)
      Returns an object of the sort described by this ValueInfo represented by the given string rep.
    • Method Detail

      • getName

        java.lang.String getName()
        Returns the name of this object.
        Returns:
        the name
      • getUnitString

        java.lang.String getUnitString()
        Returns a string representing the units of the values described by this object. The syntax and conventions should ideally match those adopted by VOTable, as defined by CDS.
        Returns:
        a string giving the units, or null if units are unknown
        See Also:
        Standards for Astronomical Catalogues: Units, CDS Strasbourg
      • getUCD

        java.lang.String getUCD()
        Returns the Unified Column Descriptor string applying to the values described by this object.
        Returns:
        the UCD, or null if none is known
        See Also:
        Unified Column Descriptor scheme, UCD
      • getUtype

        java.lang.String getUtype()
        Returns the Utype string applying to the values described by this object. Utype is a string which references a data model. It is used pervasively within IVOA standards; probably an official IVOA definition of Utype syntax and semantics will arise one day.
        Returns:
        the Utype, or null if none is known
      • getDescription

        java.lang.String getDescription()
        Returns a description of the values described by this object. It may contain a short or long textual description of the kind of information represented by the value.
        Returns:
        a textual description, or the empty string "" if there is nothing to be said
      • getContentClass

        java.lang.Class getContentClass()
        Returns the java class of the values described by this object. The intention is that any Object described by this ValueInfo will be an instance of the returned class or one of its subclasses. Note therefore that it must not return one of the primitive class objects (int.class et al.); the appropriate wrapper classes must be used instead (Integer.class etc).

        The class returned should not under normal circumstances be an array of arrays; to express multidimensionality of arrays you should store an array of non-array objects or of primitives and provide shape information via the getShape method. There is nothing to stop you describing arrays of arrays with a ValueInfo, but some other elements of the tables infrastructure and applications may work on the assumption that such objects are not present.

        Note that to store sets of more than 231 items it will be necessary to use some custom object, since java arrays are indexed by type int.

        Returns:
        the java class
      • isArray

        boolean isArray()
        Indicates whether the values described by this object are java arrays. This convenience method should return the same as
             getContentClass().getComponentType()!=null
         
        Returns:
        true iff the values described by this object are java arrays
      • getShape

        int[] getShape()
        Returns the shape associated with array value types. If the class returned by getContentClass() is a java array type, the return from this method may contain information about the shape of the rectangular array which this represents. The dimensions of the array are given in the elements of the return value of this method, fastest varying first. All elements of the array should be positive, except that the last (slowest varying) element may be <=0 (conventionally -1) to indicate that the number of (shape.length-1)-dimensional slices contained in the value is not known. If nothing is known about the shape of the array values, then a 1-element array whose only element is <=0 should be returned.

        If getContentClass does not give an array type (hence isArray returns false) the return value for this method is undefined (but should probably be null).

        Returns:
        the shape of the array value
      • getElementSize

        int getElementSize()
        May indicate the size of a value element stored as the value of this info. The total size of the value will in this case be the return value of this method multiplied by the number of elements, as indicated by getShape() (or by 1, if getShape is null).

        The exact meaning of the value returned is dependent on this ValueInfo. This method was introduced to return the maximum number of characters in a String-class ValueInfo; this information is necessary for writing out to certain formats (FITS). Other ValueInfo types however may use it for their own purposes.

        ValueInfo instances which decline to supply this information should return -1 from this method.

        Returns:
        notional size of each element an array of values described by this info
      • isNullable

        boolean isNullable()
        Indicates whether values returned described by this object may have the value null. In general this should return true, which implies no assertion about the return values (they may or may not be null). But if the values are known never to be null, it may return false.
        Returns:
        false if values are guaranteed non-null
      • getDomainMappers

        DomainMapper[] getDomainMappers()
        Returns an array of objects which may be able to convert from the values described by this info to a particular target value domain. This can used for non-obvious representations of certain coordinates such as time and angular position. In most cases the returned array will be empty, since the target domain is obvious (e.g. numeric values). In the (unusual) case that the returned array contains multiple entries, it should have no more than one for any given target domain, and the first entry may be considered "primary" in some sense. Absence of a mapper for a given target domain does not necessarily indicate that the described values cannot be used in that domain.
        Returns:
        array of domain mappers for the values described by this info
      • formatValue

        java.lang.String formatValue​(java.lang.Object value,
                                     int maxLength)
        Returns a string representation of a given value described by this ValueInfo. The returned string should be no longer than a given maximum length.
        Parameters:
        value - the value to represent
        maxLength - the maximum number of characters in the returned string
      • unformatString

        java.lang.Object unformatString​(java.lang.String rep)
        Returns an object of the sort described by this ValueInfo represented by the given string rep.
        Parameters:
        rep - the string representation of a value described by this ValueInfo
        Returns:
        the Object value represented by rep; must match this info's content class (or be null)