simpledb.query
Class FieldNameExpression

java.lang.Object
  simpledb.query.FieldNameExpression

All Implemented Interfaces:

Expression

public class FieldNameExpression
extends Object
implements Expression

An expression consisting entirely of a single field.

Author:

Edward Sciore

Constructor Summary

FieldNameExpression(String fldname)
Creates a new expression by wrapping a field.

Method Summary

boolean	appliesTo(Schema sch) Returns true if the field is in the specified schema.
Constant	asConstant() This method should never be called.
String	asFieldName() Unwraps the field name and returns it.
Constant	evaluate(Scan s) Evaluates the field by getting its value in the scan.
boolean	isConstant() Returns false.
boolean	isFieldName() Returns true.
String	toString()

Methods inherited from class java.lang.Object

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

Constructor Detail

FieldNameExpression

public FieldNameExpression(String fldname)

Creates a new expression by wrapping a field.

Parameters:

fldname - the name of the wrapped field

Method Detail

isConstant

public boolean isConstant()

Returns false.

Specified by:

isConstant in interface Expression

Returns:

true if the expression is a constant

See Also:

Expression.isConstant()

isFieldName

public boolean isFieldName()

Returns true.

Specified by:

isFieldName in interface Expression

Returns:

true if the expression denotes a field

See Also:

Expression.isFieldName()

asConstant

public Constant asConstant()

This method should never be called. Throws a ClassCastException.

Specified by:

asConstant in interface Expression

Returns:

the expression as a constant

See Also:

Expression.asConstant()

asFieldName

public String asFieldName()

Unwraps the field name and returns it.

Specified by:

asFieldName in interface Expression

Returns:

the expression as a field name

See Also:

Expression.asFieldName()

evaluate

public Constant evaluate(Scan s)

Evaluates the field by getting its value in the scan.

Specified by:

evaluate in interface Expression

Parameters:

s - the scan

Returns:

the value of the expression, as a Constant

See Also:

Expression.evaluate(simpledb.query.Scan)

appliesTo

public boolean appliesTo(Schema sch)

Returns true if the field is in the specified schema.

Specified by:

appliesTo in interface Expression

Parameters:

sch - the schema

Returns:

true if all fields in the expression are in the schema

See Also:

Expression.appliesTo(simpledb.record.Schema)

toString

public String toString()

Overrides:

toString in class Object