Class SyntheticColumn


  • public class SyntheticColumn
    extends uk.ac.starlink.table.ColumnData
    A column which produces read-only values based on an algebraic expression. This expression may include other columns in the table referenced by column name, and can use any of the java language expression constructs as well as the static methods in the java.lang.Math class. This list could be extended quite easily if new arithmetic tricks were required.

    The engine used for expression evaluation is the GNU Java Expressions Library (JEL).

    Author:
    Mark Taylor (Starlink)
    See Also:
    JEL
    • Constructor Summary

      Constructors 
      Constructor Description
      SyntheticColumn​(TopcatModel tcModel, uk.ac.starlink.table.ColumnInfo cinfo, java.lang.String expression, java.lang.Class<?> resultType)
      Constructs a new synthetic column from an algebraic expression applied to a table.
    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      java.lang.String getExpression()
      Returns the JEL expression that provides this column's value.
      java.lang.Object readValue​(long lrow)  
      void setExpression​(java.lang.String expression, java.lang.Class<?> resultType)
      Sets the algebraic expression which this column uses to calculate its results.
      • Methods inherited from class uk.ac.starlink.table.ColumnData

        getColumnInfo, isWritable, setColumnInfo, storeValue
      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
    • Constructor Detail

      • SyntheticColumn

        public SyntheticColumn​(TopcatModel tcModel,
                               uk.ac.starlink.table.ColumnInfo cinfo,
                               java.lang.String expression,
                               java.lang.Class<?> resultType)
                        throws gnu.jel.CompilationException
        Constructs a new synthetic column from an algebraic expression applied to a table.
        Parameters:
        tcModel - context for JEL expression evaluation
        cinfo - metadata for the new column; note this object may be modified as required by the supplied expression
        expression - algebraic expression for the value of this column
        resultType - a Class for the result, presumably one of the primitive wrapper types or String.class. If null a suitable class is chosen automatically.
        Throws:
        gnu.jel.CompilationException
    • Method Detail

      • setExpression

        public void setExpression​(java.lang.String expression,
                                  java.lang.Class<?> resultType)
                           throws gnu.jel.CompilationException
        Sets the algebraic expression which this column uses to calculate its results. Column names are used to refer to values of cells in other columns of this table in the same row as that for which the result is being generated.
        Parameters:
        expression - the string giving the algebraic exprssion for this column's value in terms of other columns
        resultType - a Class for the result, presumably one of the primitive wrapper types or String.class. If null a suitable class is chosen automatically.
        Throws:
        gnu.jel.CompilationException
      • getExpression

        public java.lang.String getExpression()
        Returns the JEL expression that provides this column's value.
        Returns:
        expression
      • readValue

        public java.lang.Object readValue​(long lrow)
                                   throws java.io.IOException
        Specified by:
        readValue in class uk.ac.starlink.table.ColumnData
        Throws:
        java.io.IOException