org.vanilladb.core.sql.predicate

Class ConstantExpression

java.lang.Object

org.vanilladb.core.sql.predicate.ConstantExpression

All Implemented Interfaces:

Expression

public class ConstantExpression
extends Object
implements Expression

An expression consisting entirely of a single constant.

Constructor Summary

Constructors

Constructor and Description
ConstantExpression(Constant c) Creates a new expression by wrapping a constant.

Method Summary

Modifier and Type	Method and Description
Constant	asConstant() Unwraps the constant and returns it.
String	asFieldName() This method should never be called.
Constant	evaluate(Record rec) Returns the constant, regardless of the record.
boolean	isApplicableTo(Schema sch) Returns true, because a constant applies to any schema.
boolean	isConstant() Returns true.
boolean	isFieldName() Returns false.
String	toString() Return constant value as a string.

Methods inherited from class java.lang.Object

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

Constructor Detail

ConstantExpression

public ConstantExpression(Constant c)

Creates a new expression by wrapping a constant.

Parameters:

c - the constant

Method Detail

isConstant

public boolean isConstant()

Returns true.

Specified by:

isConstant in interface Expression

Returns:

true if the expression is a constant

See Also:

Expression.isConstant()

isFieldName

public boolean isFieldName()

Returns false.

Specified by:

isFieldName in interface Expression

Returns:

true if the expression denotes a field

See Also:

Expression.isFieldName()

asConstant

public Constant asConstant()

Unwraps the constant and returns it.

Specified by:

asConstant in interface Expression

Returns:

the expression as a constant

See Also:

Expression.asConstant()

asFieldName

public String asFieldName()

This method should never be called. Throws a ClassCastException.

Specified by:

asFieldName in interface Expression

Returns:

the expression as a field name

See Also:

Expression.asFieldName()

evaluate

public Constant evaluate(Record rec)

Returns the constant, regardless of the record.

Specified by:

evaluate in interface Expression

Parameters:

rec - the record

Returns:

the value of the expression, as a constant

See Also:

Expression.evaluate(Record)

isApplicableTo

public boolean isApplicableTo(Schema sch)

Returns true, because a constant applies to any schema.

Specified by:

isApplicableTo in interface Expression

Parameters:

sch - the schema

Returns:

true if all fields in the expression are in the schema

See Also:

Expression.isApplicableTo(org.vanilladb.core.sql.Schema)

toString

public String toString()

Return constant value as a string. If the constant type is varchar, the output string will be surrounded by single quotation marks.

Overrides:

toString in class Object