relop
Class Projection

java.lang.Object
  relop.Iterator
      relop.Projection

public class Projection
extends Iterator

The projection operator extracts columns from a relation; unlike in relational algebra, this operator does NOT eliminate duplicate tuples.

Field Summary

Fields inherited from class relop.Iterator

schema

Constructor Summary

Projection(Iterator iter, java.lang.Integer... fields)
Constructs a projection, given the underlying iterator and field numbers.

Method Summary

void	close() Closes the iterator, releasing any resources (i.e.
void	explain(int depth) Gives a one-line explaination of the iterator, repeats the call on any child iterators, and increases the indent depth along the way.
Tuple	getNext() Gets the next tuple in the iteration.
boolean	hasNext() Returns true if there are more tuples, false otherwise.
boolean	isOpen() Returns true if the iterator is open; false otherwise.
void	restart() Restarts the iterator, i.e.

Methods inherited from class relop.Iterator

execute, finalize, indent

Methods inherited from class java.lang.Object

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

Constructor Detail

Projection

public Projection(Iterator iter,
                  java.lang.Integer... fields)

Constructs a projection, given the underlying iterator and field numbers.

Method Detail

explain

public void explain(int depth)

Gives a one-line explaination of the iterator, repeats the call on any child iterators, and increases the indent depth along the way.

Specified by:

explain in class Iterator

restart

public void restart()

Restarts the iterator, i.e. as if it were just constructed.

Specified by:

restart in class Iterator

isOpen

public boolean isOpen()

Returns true if the iterator is open; false otherwise.

Specified by:

isOpen in class Iterator

close

public void close()

Closes the iterator, releasing any resources (i.e. pinned pages).

Specified by:

close in class Iterator

hasNext

public boolean hasNext()

Returns true if there are more tuples, false otherwise.

Specified by:

hasNext in class Iterator

getNext

public Tuple getNext()

Gets the next tuple in the iteration.

Specified by:

getNext in class Iterator

Throws:

java.lang.IllegalStateException - if no more tuples