org.josql.expressions
Class Function

java.lang.Object
  org.josql.expressions.Expression
      org.josql.expressions.ValueExpression
          org.josql.expressions.Function

public class Function
extends ValueExpression

This class represents a Function that can be "called" in JoSQL.

Constructor Summary

Function()

Method Summary

Object	evaluate(Object o, Query q) Evaluate this function on the current object.
String	getAccessor()
Class	getExpectedReturnType(Query q) Get the expected return type from the function.
com.gentlyweb.utils.Getter	getGetter()
String	getName()
List	getParameters() Return the List of Expression objects that constitute the arguments to the function, no guarantee is made here as to whether they have been inited.
boolean	hasFixedResult(Query q) Return whether the function will return a fixed result, this only occurs iff all the arguments to the function also return a fixed result.
void	init(Query q) This is a complex method that will initialise the function.
boolean	isTrue(Object o, Query q) Return whether the evaluation of this function (see: evaluate(Object,Query)) will result in a true value.
void	setAccessor(String acc)
void	setName(String name)
void	setParameters(List ps)
String	toString() Return a string representation of the function.

Methods inherited from class org.josql.expressions.ValueExpression

getValue

Methods inherited from class org.josql.expressions.Expression

isBracketed, setBracketed

Methods inherited from class java.lang.Object

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

Constructor Detail

Function

public Function()

Method Detail

getGetter

public com.gentlyweb.utils.Getter getGetter()

getAccessor

public String getAccessor()

setAccessor

public void setAccessor(String acc)

getExpectedReturnType

public Class getExpectedReturnType(Query q)

Get the expected return type from the function. The exact class returned is dependent upon the function (Java method) that is being called.

Specified by:

getExpectedReturnType in class Expression

Parameters:

q - The Query object.

Returns:

The class of the expected return type.

init

public void init(Query q)
          throws QueryParseException

This is a complex method that will initialise the function. Firstly all of the "arguments" to the function are inited and then their expected return types gained from calling: getExpectedReturnType(Query). Then the function handlers, user-defined and then built-in are searched until they find a match for the function name, ensure that it's a public method and that all the arguments match, widening the match where necessary.

Specified by:

init in class Expression

Parameters:

q - The Query object.

Throws:

QueryParseException - If something goes wrong whilst initing the arguments to the function or if the function cannot be found.

getParameters

public List getParameters()

Return the List of Expression objects that constitute the arguments to the function, no guarantee is made here as to whether they have been inited.

Returns:

The List of Expression objects.

setParameters

public void setParameters(List ps)

setName

public void setName(String name)

getName

public String getName()

evaluate

public Object evaluate(Object o,
                       Query q)
                throws QueryExecutionException

Evaluate this function on the current object. It should be noted that not all functions will use the current object in their execution, functions from the GroupingFunctions class are notable exceptions.

Specified by:

evaluate in class ValueExpression

Parameters:

o - The current object.

q - The Query object.

Returns:

The result of evaluating the function.

Throws:

QueryExecutionException - If something goes wrong during execution of the function or gaining the values to be used as arguments.

isTrue

public boolean isTrue(Object o,
                      Query q)
               throws QueryExecutionException

Return whether the evaluation of this function (see: evaluate(Object,Query)) will result in a true value. See: ArithmeticExpression.isTrue(Object,Query) for details of how this is determined.

Specified by:

isTrue in class Expression

Parameters:

o - The current object.

q - The Query object.

Returns:

true if the function return value evaluates to true.

Throws:

QueryExecutionException - If something goes wrong with evaluating the function.

toString

public String toString()

Return a string representation of the function. In the form: Name ( Expression [ , Expression ] )

Specified by:

toString in class Expression

Returns:

A string representation of the function.

hasFixedResult

public boolean hasFixedResult(Query q)

Return whether the function will return a fixed result, this only occurs iff all the arguments to the function also return a fixed result.

Specified by:

hasFixedResult in class Expression

Parameters:

q - The Query object.

Returns:

true if the expression evaluates to a fixed/constant result.