relop
Class Iterator

java.lang.Object
  relop.Iterator

Direct Known Subclasses:

FileScan, HashJoin, IndexScan, KeyScan, Projection, Selection, SimpleJoin

public abstract class Iterator
extends java.lang.Object

Minibase Iterators

Query execution is driven by a tree of relational operators, all of which are implemented as iterators. Results are requested by successive "get next tuple" calls on the root of the tree, which in turn makes similar calls to child iterators throughout the tree. Intermediate nodes (i.e. join iterators) drive the leaf-level nodes (i.e. file or index scan iterators).

Field Summary

protected Schema

schema Schema for resulting tuples; must be set in all subclass constructors.

Constructor Summary

Iterator()

Method Summary

abstract void	close() Closes the iterator, releasing any resources (i.e.
int	execute() Prints the schema, gets and prints all tuples, and closes the iterator.
abstract 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.
protected void	finalize() Called by the garbage collector when there are no more references to the object; closes the iterator if it's still open.
abstract Tuple	getNext() Gets the next tuple in the iteration.
abstract boolean	hasNext() Returns true if there are more tuples, false otherwise.
protected void	indent(int depth) Outputs the indentation for the given depth.
abstract boolean	isOpen() Returns true if the iterator is open; false otherwise.
abstract void	restart() Restarts the iterator, i.e.

Methods inherited from class java.lang.Object

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

Field Detail

schema

protected Schema schema

Schema for resulting tuples; must be set in all subclass constructors.

Constructor Detail

Iterator

public Iterator()

Method Detail

explain

public abstract 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.

indent

protected void indent(int depth)

Outputs the indentation for the given depth.

restart

public abstract void restart()

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

isOpen

public abstract boolean isOpen()

Returns true if the iterator is open; false otherwise.

close

public abstract void close()

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

hasNext

public abstract boolean hasNext()

Returns true if there are more tuples, false otherwise.

getNext

public abstract Tuple getNext()

Gets the next tuple in the iteration.

Throws:

java.lang.IllegalStateException - if no more tuples

execute

public int execute()

Prints the schema, gets and prints all tuples, and closes the iterator.

Returns:

number of tuples processed

finalize

protected void finalize()
                 throws java.lang.Throwable

Called by the garbage collector when there are no more references to the object; closes the iterator if it's still open.

Overrides:

finalize in class java.lang.Object

Throws:

java.lang.Throwable