simpledb.materialize
Class SortScan

java.lang.Object
  simpledb.materialize.SortScan

All Implemented Interfaces:

Scan

public class SortScan
extends Object
implements Scan

Author:

sciore

Constructor Summary

SortScan(List<TempTable> runs, RecordComparator comp)
Creates a sort scan, given a list of 1 or 2 runs.

Method Summary

void	beforeFirst() Positions the scan before the first record in sorted order.
void	close() Closes the two underlying scans.
int	getInt(String fldname) Gets the integer value of the specified field of the current scan.
String	getString(String fldname) Gets the string value of the specified field of the current scan.
Constant	getVal(String fldname) Gets the Constant value of the specified field of the current scan.
boolean	hasField(String fldname) Returns true if the specified field is in the current scan.
boolean	next() Moves to the next record in sorted order.
void	restorePosition() Moves the scan to its previously-saved position.
void	savePosition() Saves the position of the current record, so that it can be restored at a later time.

Methods inherited from class java.lang.Object

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

Constructor Detail

SortScan

public SortScan(List<TempTable> runs,
                RecordComparator comp)

Creates a sort scan, given a list of 1 or 2 runs. If there is only 1 run, then s2 will be null and hasmore2 will be false.

Parameters:

runs - the list of runs

comp - the record comparator

Method Detail

beforeFirst

public void beforeFirst()

Positions the scan before the first record in sorted order. Internally, it moves to the first record of each underlying scan. The variable currentscan is set to null, indicating that there is no current scan.

Specified by:

beforeFirst in interface Scan

See Also:

Scan.beforeFirst()

next

public boolean next()

Moves to the next record in sorted order. First, the current scan is moved to the next record. Then the lowest record of the two scans is found, and that scan is chosen to be the new current scan.

Specified by:

next in interface Scan

Returns:

false if there is no next record

See Also:

Scan.next()

close

public void close()

Closes the two underlying scans.

Specified by:

close in interface Scan

See Also:

Scan.close()

getVal

public Constant getVal(String fldname)

Gets the Constant value of the specified field of the current scan.

Specified by:

getVal in interface Scan

Parameters:

fldname - the name of the field

Returns:

the value of that field, expressed as a Constant.

See Also:

Scan.getVal(java.lang.String)

getInt

public int getInt(String fldname)

Gets the integer value of the specified field of the current scan.

Specified by:

getInt in interface Scan

Parameters:

fldname - the name of the field

Returns:

the field's integer value in the current record

See Also:

Scan.getInt(java.lang.String)

getString

public String getString(String fldname)

Gets the string value of the specified field of the current scan.

Specified by:

getString in interface Scan

Parameters:

fldname - the name of the field

Returns:

the field's string value in the current record

See Also:

Scan.getString(java.lang.String)

hasField

public boolean hasField(String fldname)

Returns true if the specified field is in the current scan.

Specified by:

hasField in interface Scan

Parameters:

fldname - the name of the field

Returns:

true if the scan has that field

See Also:

Scan.hasField(java.lang.String)

savePosition

public void savePosition()

Saves the position of the current record, so that it can be restored at a later time.

restorePosition

public void restorePosition()

Moves the scan to its previously-saved position.