simpledb.query
Class ProductScan

java.lang.Object
  simpledb.query.ProductScan

All Implemented Interfaces:

Scan

public class ProductScan
extends java.lang.Object
implements Scan

The scan class corresponding to the product relational algebra operator.

Author:

Edward Sciore

Constructor Summary

ProductScan(Scan s1, Scan s2)
Creates a product scan having the two underlying scans.

Method Summary

void	beforeFirst() Positions the scan before its first record.
void	close() Closes both underlying scans.
int	getInt(java.lang.String fldname) Returns the integer value of the specified field.
java.lang.String	getString(java.lang.String fldname) Returns the string value of the specified field.
Constant	getVal(java.lang.String fldname) Returns the value of the specified field.
boolean	hasField(java.lang.String fldname) Returns true if the specified field is in either of the underlying scans.
boolean	next() Moves the scan to the next record.

Methods inherited from class java.lang.Object

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

Constructor Detail

ProductScan

public ProductScan(Scan s1,
                   Scan s2)

Creates a product scan having the two underlying scans.

Parameters:

s1 - the LHS scan

s2 - the RHS scan

Method Detail

beforeFirst

public void beforeFirst()

Positions the scan before its first record. In other words, the LHS scan is positioned at its first record, and the RHS scan is positioned before its first record.

Specified by:

beforeFirst in interface Scan

See Also:

Scan.beforeFirst()

next

public boolean next()

Moves the scan to the next record. The method moves to the next RHS record, if possible. Otherwise, it moves to the next LHS record and the first RHS record. If there are no more LHS records, the method returns false.

Specified by:

next in interface Scan

Returns:

false if there is no next record

See Also:

Scan.next()

close

public void close()

Closes both underlying scans.

Specified by:

close in interface Scan

See Also:

Scan.close()

getVal

public Constant getVal(java.lang.String fldname)

Returns the value of the specified field. The value is obtained from whichever scan contains the field.

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(java.lang.String fldname)

Returns the integer value of the specified field. The value is obtained from whichever scan contains the field.

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 java.lang.String getString(java.lang.String fldname)

Returns the string value of the specified field. The value is obtained from whichever scan contains the field.

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(java.lang.String fldname)

Returns true if the specified field is in either of the underlying scans.

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)