Next Previous Up Contents
Next: Add a new column
Up: Examples
Previous: Sorted Table

6.4.2 Turn a set of arrays into a StarTable

Suppose you have three arrays representing a set of points on the plane, giving an index number and an x and y coordinate, and you would like to manipulate them as a StarTable. One way is to use the ColumnStarTable class, which gives you a table of a specified number of rows but initially no columns, to which you can add data a column at a time. Each added column is an instance of ColumnData; the ArrayColumn class provides a convenient implementation which wraps an array of objects or primitives (one element per row).

    StarTable makeTable( int[] index, double[] x, double[] y ) {
        int nRow = index.length;
        ColumnStarTable table = ColumnStarTable.makeTableWithRows( nRow );
        table.addColumn( ArrayColumn.makeColumn( "Index", index ) );
        table.addColumn( ArrayColumn.makeColumn( "x", x ) );
        table.addColumn( ArrayColumn.makeColumn( "y", y ) );
        return table;

A more general way to approach this is to write a new implementation of StarTable; this is like what happens in Swing if you write your own TableModel to provide data for a JTable. In order to do this you will usually want to subclass one of the existing implementations, probably AbstractStarTable, RandomStarTable or WrapperStarTable. Here is how it can be done:

    class PointsStarTable extends RandomStarTable {

        // Define the metadata object for each of the columns.
        ColumnInfo[] colInfos_ = new ColumnInfo[] {
            new ColumnInfo( "Index", Integer.class, "point index" ),
            new ColumnInfo( "X", Double.class, "x co-ordinate" ),
            new ColumnInfo( "Y", Double.class, "y co-ordinate" ),

        // Member variables are arrays holding the actual data.
        int[] index_;
        double[] x_;
        double[] y_;
        long nRow_;

        public PointsStarTable( int[] index, double[] x, double[] y ) {
            index_ = index;
            x_ = x;
            y_ = y;
            nRow_ = (long) index_.length;

        public int getColumnCount() {
            return 3;

        public long getRowCount() {
            return nRow_;

        public ColumnInfo getColumnInfo( int icol ) {
            return colInfos_[ icol ];

        public Object getCell( long lrow, int icol ) {
            int irow = checkedLongToInt( lrow );
            switch ( icol ) {
                case 0: return new Integer( index_[ irow ] );
                case 1: return new Double( x_[ irow ] );
                case 2: return new Double( y_[ irow ] );
                default: throw new IllegalArgumentException();
In this case it is only necessary to implement the getCell method; RandomStarTable implements the other data access methods (getRow, getRowSequence, getRowAccess) in terms of this. Note that for more complicated behaviour, more methods may need to be implemented.

Next Previous Up Contents
Next: Add a new column
Up: Examples
Previous: Sorted Table

STIL - Starlink Tables Infrastructure Library
Starlink User Note252
STIL web page:
Author email: