simpledb

Class Operator

java.lang.Object

simpledb.Operator

All Implemented Interfaces:

java.io.Serializable, DbIterator

Direct Known Subclasses:

Aggregate, Delete, Filter, HashEquiJoin, Insert, Join, OrderBy, Project

public abstract class Operator
extends java.lang.Object
implements DbIterator

Abstract class for implementing operators. It handles close, next and hasNext. Subclasses only need to implement open and readNext.

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
private int	estimatedCardinality
private Tuple	next
private boolean	open
private static long	serialVersionUID

Constructor Summary

Constructors

Constructor and Description
Operator()

Method Summary

Modifier and Type	Method and Description
void	close() Closes this iterator.
protected abstract Tuple	fetchNext() Returns the next Tuple in the iterator, or null if the iteration is finished.
abstract DbIterator[]	getChildren()
int	getEstimatedCardinality()
abstract TupleDesc	getTupleDesc() Returns the TupleDesc associated with this DbIterator.
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.
abstract void	setChildren(DbIterator[] children) Set the children(child) of this operator.
protected void	setEstimatedCardinality(int card)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface simpledb.DbIterator

rewind

Field Detail

serialVersionUID

private static final long serialVersionUID

See Also:

Constant Field Values

next

private Tuple next

open

private boolean open

estimatedCardinality

private int estimatedCardinality

Constructor Detail

Operator

public Operator()

Method Detail

hasNext

public boolean hasNext()
                throws DbException,
                       TransactionAbortedException

Description copied from interface: DbIterator

Returns true if the iterator has more tuples.

Specified by:

hasNext in interface DbIterator

Returns:

true f the iterator has more tuples.

Throws:

DbException

TransactionAbortedException

next

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

Description copied from interface: DbIterator

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

Specified by:

next in interface DbIterator

Returns:

the next tuple in the iteration.

Throws:

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

DbException

TransactionAbortedException

fetchNext

protected abstract Tuple fetchNext()
                            throws DbException,
                                   TransactionAbortedException

Returns the next Tuple in the iterator, or null if the iteration is finished. Operator uses this method to implement both next and hasNext.

Returns:

the next Tuple in the iterator, or null if the iteration is finished.

Throws:

DbException

TransactionAbortedException

close

public void close()

Closes this iterator. If overridden by a subclass, they should call super.close() in order for Operator's internal state to be consistent.

Specified by:

close in interface DbIterator

open

public void open()
          throws DbException,
                 TransactionAbortedException

Description copied from interface: DbIterator

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

Specified by:

open in interface DbIterator

Throws:

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

TransactionAbortedException

getChildren

public abstract DbIterator[] getChildren()

Returns:

return the children DbIterators of this operator. If there is only one child, return an array of only one element. For join operators, the order of the children is not important. But they should be consistent among multiple calls.

setChildren

public abstract void setChildren(DbIterator[] children)

Set the children(child) of this operator. If the operator has only one child, children[0] should be used. If the operator is a join, children[0] and children[1] should be used.

Parameters:

children - the DbIterators which are to be set as the children(child) of this operator

getTupleDesc

public abstract TupleDesc getTupleDesc()

Description copied from interface: DbIterator

Returns the TupleDesc associated with this DbIterator.

Specified by:

getTupleDesc in interface DbIterator

Returns:

return the TupleDesc of the output tuples of this operator

getEstimatedCardinality

public int getEstimatedCardinality()

Returns:

The estimated cardinality of this operator.

setEstimatedCardinality

protected void setEstimatedCardinality(int card)

Parameters:

card - The estimated cardinality of this operator.