ps3

/*
 * CrossIterator.java
 *
 * DBMS Implementation
 */

import java.io.*;
import com.sleepycat.db.*;

/**
 * A class that serves as an iterator over some or all of the tuples
 * in the cross product (i.e., Cartesian product) of two or more
 * tables.
 */
public class CrossIterator extends RelationIterator {
    private TableIterator[] tableIter;
    private Column[] columns;
    private ConditionalExpression where;
    private int numTuples;


    /**
     * Constructs a CrossIterator object for the subset of the cross
     * product specified by the given SQLStatement.  If the
     * SQLStatement has a WHERE clause, the iterator will only visit
     * rows that satisfy the WHERE clause.
     *
     * @param  stmt  the SQL statement that specifies the cross product
     * @throws IllegalStateException if one of the Table objects in stmt
     *         has not already been opened
     * @throws DatabaseException if Berkeley DB encounters a problem
     *         while accessing one of the underlying database(s)
     */
    public CrossIterator(SQLStatement stmt) throws DatabaseException {
        /* not yet implemented */
        int sizeOfcolArry = 0;
        int colIndex = 0;

        /**
         * loop to get sum of columns from each table
         * in order to dynamicaly size columns array
         */
        for (int i = 0; i < stmt.numTables(); i++) {
             Table t = new Table(stmt.getTable(i).getName());
             t.open();
            sizeOfcolArry += t.numColumns();                     // count number of columns in each table

        }

        this.columns = new Column[sizeOfcolArry];
        this.tableIter = new TableIterator[stmt.numTables()];
        /* *
         *   loop over num tables in the stmt
         */
        for (int i = 0; i < stmt.numTables(); i++) {
            stmt.getTable(i).open();
            TableIterator iter = new TableIterator(stmt,stmt.getTable(i),false);

            tableIter[i] = iter;                                 // assign iter to tableIter array
            /**
             * loop to store column objects into column array
             */
            for (int j = 0; j < stmt.getTable(i).numColumns(); j++) {
                this.columns[colIndex] = stmt.getTable(i).getColumn(j);
                this.columns[colIndex].setTableIterator(iter);
                colIndex++;
            }
        }

        this.where = stmt.getWhere();
        if (this.where == null)
            this.where = new TrueExpression();   // set were clause

        this.numTuples = 0;
    }

    /**
     * Closes the iterator, which closes any BDB handles that it is using.
     *
     * @throws DatabaseException if Berkeley DB encounters a problem
     *         while closing a handle
     */
    public void close() throws DatabaseException {
        /* not yet implemented */
         for (int i = 0; i < tableIter.length; i++) {
            tableIter[i].close();
        }
    }

    /**
     * Advances the iterator to the next tuple in the relation.  If
     * there is a WHERE clause that limits which tuples should be
     * included in the relation, this method will advance the iterator
     * to the next tuple that satisfies the WHERE clause.  If the
     * iterator is newly created, this method will position it on the first
     * tuple in the relation (that satisfies the WHERE clause).
     *
     * @return true if the iterator was advanced to a new tuple, and false
     *         if there are no more tuples to visit
     * @throws DeadlockException if deadlock occurs while accessing the
     *         underlying BDB database(s)
     * @throws DatabaseException if Berkeley DB encounters another problem
     *         while accessing the underlying database(s)
     */
    public boolean next() throws DeadlockException, DatabaseException {
        /* not yet implemented */

                if (numTuples == 0) {
                   if (!tableIter[0].first())
                       return false;   // R is empty
                }

                // Advance the table iterators as much as needed to get
                // to a combination of rows from R and S that satisfies the
                // WHERE clause.
                do {


                    if (!tableIter[1].next()) {

                        // We've paired all rows of S with the current row of R,
                        // so reset S to its first row...
                        if (!tableIter[1].first()){
                            return false;   // S is empty
                        }
                        // ...and advance to R's next row (if any).
                        if (!tableIter[0].next())
                            return false;   // no more rows in R, so we're done
                    }

                 } while(!this.where.isTrue());

        this.numTuples++;
        return true;
    }

    /**
     * Gets the column at the specified index in the relation that
     * this iterator iterates over.  The leftmost column has an index of 0.
     *
     * @return  the column
     * @throws  IndexOutOfBoundsException if the specified index is invalid
     */
    public Column getColumn(int colIndex) {
        /* not yet implemented */
        return this.columns[colIndex];
    }

    /**
     * Gets the value of the column at the specified index in the row
     * on which this iterator is currently positioned.  The leftmost
     * column has an index of 0.
     *
     * This method will unmarshall the relevant bytes from the
     * key/data pair and return the corresponding Object -- i.e.,
     * an object of type String for CHAR and VARCHAR values, an object
     * of type Integer for INTEGER values, or an object of type Double
     * for REAL values.
     *
     * @return  the value of the column
     * @throws IllegalStateException if the iterator has not yet been
     *         been positioned on a tuple using first() or next()
     * @throws  IndexOutOfBoundsException if the specified index is invalid
     */
    public Object getColumnVal(int colIndex) {
        /* not yet implemented */
        return columns[colIndex].getTableIterator().getColumnVal(colIndex);
    }

    public int numColumns() {
        return this.columns.length;
    }

    public int numTuples() {
        return this.numTuples;
    }
}




output

 | name                 | enrollment  | course               | location   |
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 | CS 165               | 31         Index: 2, Size: 2.