2.6. Operators

public class SeqScan implements DbIterator {

    private static final long serialVersionUID = 1L;
    TransactionId tid;
    int tableid;
    String tableAlia;
    DbFile dbFile;
    DbFileIterator dbFileIterator;




    /**
     * Creates a sequential scan over the specified table as a part of the
     * specified transaction.
     *
     * @param tid
     *            The transaction this scan is running as a part of.
     * @param tableid
     *            the table to scan.
     * @param tableAlias
     *            the alias of this table (needed by the parser); the returned
     *            tupleDesc should have fields with name tableAlias.fieldName
     *            (note: this class is not responsible for handling a case where
     *            tableAlias or fieldName are null. It shouldn't crash if they
     *            are, but the resulting name can be null.fieldName,
     *            tableAlias.null, or null.null).
     */
    public SeqScan(TransactionId tid, int tableid, String tableAlias) {
        // some code goes here

        this.tid =tid;
        this.tableid = tableid;
        this.tableAlia = tableAlias;

        dbFile = Database.getCatalog().getDbFile(tableid);
    }

    /**
     * @return
     *       return the table name of the table the operator scans. This should
     *       be the actual name of the table in the catalog of the database
     * */
    public String getTableName() {
        return Database.getCatalog().getTableName(tableid);
    }

    /**
     * @return Return the alias of the table this operator scans.
     * */
    public String getAlias()
    {
        // some code goes here
        return tableAlia;

    }

    /**
     * Reset the tableid, and tableAlias of this operator.
     * @param tableid
     *            the table to scan.
     * @param tableAlias
     *            the alias of this table (needed by the parser); the returned
     *            tupleDesc should have fields with name tableAlias.fieldName
     *            (note: this class is not responsible for handling a case where
     *            tableAlias or fieldName are null. It shouldn't crash if they
     *            are, but the resulting name can be null.fieldName,
     *            tableAlias.null, or null.null).
     */
    public void reset(int tableid, String tableAlias) {
        Database.getCatalog().getTable(tableid).tupleDesc.tableAlias = tableAlias;
        // some code goes here
    }

    public SeqScan(TransactionId tid, int tableid) {
        this(tid, tableid, Database.getCatalog().getTableName(tableid));
    }

    public void open() throws DbException, TransactionAbortedException {

        dbFileIterator.open();

    }

    /**
     * Returns the TupleDesc with field names from the underlying HeapFile,
     * prefixed with the tableAlias string from the constructor. This prefix
     * becomes useful when joining tables containing a field(s) with the same
     * name.
     *
     * @return the TupleDesc with field names from the underlying HeapFile,
     *         prefixed with the tableAlias string from the constructor.
     */
    public TupleDesc getTupleDesc() {
        // some code goes here
        return Database.getCatalog().getTupleDesc(tableid);
    }

    public boolean hasNext() throws TransactionAbortedException, DbException {


        // some code goes here


        return dbFileIterator.hasNext();

    }

    public Tuple next() throws NoSuchElementException,
            TransactionAbortedException, DbException {
        return dbFileIterator.next();
    }

    public void close() {
        // some code goes here
        dbFileIterator=null;

    }

    public void rewind() throws DbException, NoSuchElementException,
            TransactionAbortedException {
        // some code goes here

    }
}