org.josql.expressions
Class ArithmeticExpression

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

public class ArithmeticExpression
extends ValueExpression

Represents the arithmetic expressions: *, +, /, - and %. It should be noted that ALL numbers in JoSQL are represented as double values, this allows for easy arithmetic operations without the fear of losing precision or casting issues.

Field Summary

static int	ADDITION
static int	DIVIDE
static int	MODULUS
static int	MULTIPLY
static int	SUBTRACT

Constructor Summary

ArithmeticExpression()

Method Summary

Object	evaluate(Object o, Query q) Evaulate this expression.
Class	getExpectedReturnType(Query q) Return the expected return type.
ValueExpression	getLeft() Get the LHS value expression.
ValueExpression	getRight() Get the RHS value expression.
int	getType()
boolean	hasFixedResult(Query q) Return whether this expression has a fixed result.
void	init(Query q) Perform the necessary initialisation for this expression.
boolean	isTrue(Object o, Query q) Determine whether this arithmetic expression evaluates to true.
void	setLeft(ValueExpression exp)
void	setRight(ValueExpression exp)
void	setType(int t)
String	toString() Return a string representation of the expression, making this abstract forces sub-classes to provide an implementation.

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

Field Detail

MULTIPLY

public static final int MULTIPLY

See Also:

Constant Field Values

ADDITION

public static final int ADDITION

See Also:

Constant Field Values

SUBTRACT

public static final int SUBTRACT

See Also:

Constant Field Values

DIVIDE

public static final int DIVIDE

See Also:

Constant Field Values

MODULUS

public static final int MODULUS

See Also:

Constant Field Values

Constructor Detail

ArithmeticExpression

public ArithmeticExpression()

Method Detail

getExpectedReturnType

public Class getExpectedReturnType(Query q)
                            throws QueryParseException

Return the expected return type. This just returns the result of calling this method on the LHS.

Specified by:

getExpectedReturnType in class Expression

Parameters:

q - The Query object.

Returns:

The expected return type class.

Throws:

QueryParseException - If something goes wrong in determining the return type.

isTrue

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

Determine whether this arithmetic expression evaluates to true. Whilst this seems a little bizarre this method is needed to allow artithmetic expressions to be used in the columns part of the SELECT.

Thus the following could be performed:

   SELECT 10 + 20
   FROM   java.lang.Object
 

The rules are as follows:

• If evaluate(Object,Query) returns null then false is returned.
• If evaluate(Object,Query) returns a number and it is greater than 0 then true is returned. If it is 0 or less than 0 then false is returned.
• If it is anything else then true is returned.

Specified by:

isTrue in class Expression

Parameters:

o - The object to perform the expression on.

q - The Query object.

Returns:

As according to the rules above.

Throws:

QueryExecutionException - If something goes wrong during the evaluation of the expression.

hasFixedResult

public boolean hasFixedResult(Query q)

Return whether this expression has a fixed result.

Specified by:

hasFixedResult in class Expression

Parameters:

q - The Query object.

Returns:

LHS.hasFixedResult(Query) && RHS.hasFixedResult(Query)

init

public void init(Query q)
          throws QueryParseException

Description copied from class: Expression

Perform the necessary initialisation for this expression. The exact operations performed are defined by the sub-class.

Specified by:

init in class Expression

Parameters:

q - The Query object.

Throws:

QueryParseException - If something goes wrong with the initialisation.

getRight

public ValueExpression getRight()

Get the RHS value expression.

Returns:

The RHS.

getLeft

public ValueExpression getLeft()

Get the LHS value expression.

Returns:

The LHS.

setLeft

public void setLeft(ValueExpression exp)

setRight

public void setRight(ValueExpression exp)

getType

public int getType()

setType

public void setType(int t)

evaluate

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

Evaulate this expression. Apart from the special cases the LHS and RHS must evaluate to an instance of java.lang.Number otherwise a QueryExecutionException is thrown.

Special cases:

• If the type of the expression is + and either LHS or RHS are NOT numbers then the String concatentation of them both are returned. This works the same as in Java.
• If the type of the expression is / and the RHS is 0 then 0 is returned.

Specified by:

evaluate in class ValueExpression

Parameters:

o - The object to perform the expression on.

q - The Query object.

Returns:

The result of the expression, see the "special cases" for the exceptions to what would be the intuitive result.

Throws:

QueryExecutionException - If an error occurs during processing.

toString

public String toString()

Description copied from class: Expression

Return a string representation of the expression, making this abstract forces sub-classes to provide an implementation.

Specified by:

toString in class Expression

Returns:

A string representation of the expression.