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package simpledb;

import java.io.Serializable;

import java.util.*;

/**

* DbIterator 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.

*/

public interface DbIterator extends Serializable{

/**

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

* @throws DbException when there are problems opening/accessing the database.

*/

public void open()

throws DbException, TransactionAbortedException;

/** Returns true if the iterator has more tuples.

* @return true f the iterator has more tuples.

* @throws IllegalStateException If the iterator has not been opened

*/

public boolean hasNext() throws DbException, TransactionAbortedException;

/**

* Returns the next tuple from the operator (typically implementing by reading

* from a child operator or an access method).

*

* @return the next tuple in the iteration.

* @throws NoSuchElementException if there are no more tuples.

* @throws IllegalStateException If the iterator has not been opened

*/

public Tuple next() throws DbException, TransactionAbortedException, NoSuchElementException;

/**

* Resets the iterator to the start.

* @throws DbException when rewind is unsupported.

* @throws IllegalStateException If the iterator has not been opened

*/

public void rewind() throws DbException, TransactionAbortedException;

/**

* Returns the TupleDesc associated with this DbIterator.

* @return the TupleDesc associated with this DbIterator.

*/

public TupleDesc getTupleDesc();

/**

* Closes the iterator. When the iterator is closed, calling next(),

* hasNext(), or rewind() should fail by throwing IllegalStateException.

*/

public void close();

}