simpledb.query
Interface Expression

All Known Implementing Classes:

ConstantExpression, FieldNameExpression

public interface Expression

The interface corresponding to SQL expressions.

Author:

Edward Sciore

Method Summary

boolean	appliesTo(Schema sch) Determines if all of the fields mentioned in this expression are contained in the specified schema.
Constant	asConstant() Returns the constant corresponding to a constant expression.
String	asFieldName() Returns the field name corresponding to a constant expression.
Constant	evaluate(Scan s) Evaluates the expression with respect to the current record of the specified scan.
boolean	isConstant() Returns true if the expression is a constant.
boolean	isFieldName() Returns true if the expression is a field reference.

Method Detail

isConstant

boolean isConstant()

Returns true if the expression is a constant.

Returns:

true if the expression is a constant

isFieldName

boolean isFieldName()

Returns true if the expression is a field reference.

Returns:

true if the expression denotes a field

asConstant

Constant asConstant()

Returns the constant corresponding to a constant expression. Throws an exception if the expression does not denote a constant.

Returns:

the expression as a constant

asFieldName

String asFieldName()

Returns the field name corresponding to a constant expression. Throws an exception if the expression does not denote a field.

Returns:

the expression as a field name

evaluate

Constant evaluate(Scan s)

Evaluates the expression with respect to the current record of the specified scan.

Parameters:

s - the scan

Returns:

the value of the expression, as a Constant

appliesTo

boolean appliesTo(Schema sch)

Determines if all of the fields mentioned in this expression are contained in the specified schema.

Parameters:

sch - the schema

Returns:

true if all fields in the expression are in the schema