simpledb

Interface OpIterator

All Superinterfaces:

java.io.Serializable

All Known Implementing Classes:

SeqScan, TupleIterator

public interface OpIterator
extends java.io.Serializable

OpIterator is the iterator interface that all SimpleDB operators should implement. If the iterator is not open, none of the methods should work, and should throw an IllegalStateException. In addition to any resource allocation/deallocation, an open method should call any child iterator open methods, and in a close method, an iterator should call its children's close methods.

Method Summary

Modifier and Type	Method and Description
void	close() Closes the iterator.
TupleDesc	getTupleDesc() Returns the TupleDesc associated with this OpIterator.
boolean	hasNext() Returns true if the iterator has more tuples.
Tuple	next() Returns the next tuple from the operator (typically implementing by reading from a child operator or an access method).
void	open() Opens the iterator.
void	rewind() Resets the iterator to the start.

Method Detail

open

void open()
   throws DbException,
          TransactionAbortedException

Opens the iterator. This must be called before any of the other methods.

Throws:

DbException - when there are problems opening/accessing the database.

TransactionAbortedException

hasNext

boolean hasNext()
         throws DbException,
                TransactionAbortedException

Returns true if the iterator has more tuples.

Returns:

true f the iterator has more tuples.

Throws:

java.lang.IllegalStateException - If the iterator has not been opened

DbException

TransactionAbortedException

next

Tuple next()
    throws DbException,
           TransactionAbortedException,
           java.util.NoSuchElementException

Returns the next tuple from the operator (typically implementing by reading from a child operator or an access method).

Returns:

the next tuple in the iteration.

Throws:

java.util.NoSuchElementException - if there are no more tuples.

java.lang.IllegalStateException - If the iterator has not been opened

DbException

TransactionAbortedException

rewind

void rewind()
     throws DbException,
            TransactionAbortedException

Resets the iterator to the start.

Throws:

DbException - when rewind is unsupported.

java.lang.IllegalStateException - If the iterator has not been opened

TransactionAbortedException

getTupleDesc

TupleDesc getTupleDesc()

Returns the TupleDesc associated with this OpIterator.

Returns:

the TupleDesc associated with this OpIterator.

close

void close()

Closes the iterator. When the iterator is closed, calling next(), hasNext(), or rewind() should fail by throwing IllegalStateException.