org.josql.expressions

类 ArithmeticExpression

java.lang.Object

org.josql.expressions.Expression

org.josql.expressions.ValueExpression

org.josql.expressions.ArithmeticExpression

public class ArithmeticExpression
extends ValueExpression

字段概要

字段

限定符和类型	字段和说明
static int	ADDITION
static int	DIVIDE
static int	MODULUS
static int	MULTIPLY
static int	SUBTRACT

构造器概要

构造器

构造器和说明
ArithmeticExpression()

方法概要

限定符和类型	方法和说明
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 the expression will evaluate to a fixed/constant 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.

从类继承的方法 org.josql.expressions.ValueExpression

getValue

从类继承的方法 org.josql.expressions.Expression

isBracketed, setBracketed

从类继承的方法 java.lang.Object

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

字段详细资料

MULTIPLY

public static final int MULTIPLY

另请参阅:

常量字段值

ADDITION

public static final int ADDITION

另请参阅:

常量字段值

SUBTRACT

public static final int SUBTRACT

另请参阅:

常量字段值

DIVIDE

public static final int DIVIDE

另请参阅:

常量字段值

MODULUS

public static final int MODULUS

另请参阅:

常量字段值

构造器详细资料

ArithmeticExpression

public ArithmeticExpression()

方法详细资料

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.

指定者:

getExpectedReturnType 在类中 Expression

参数:

q - The Query object.

返回:

The expected return type class.

抛出:

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.

指定者:

isTrue 在类中 Expression

参数:

o - The object to perform the expression on.

q - The Query object.

返回:

As according to the rules above.

抛出:

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

hasFixedResult

public boolean hasFixedResult(Query q)

从类复制的说明: Expression

Return whether the expression will evaluate to a fixed/constant result. This allows certain optimisations to be performed when an expression is evaluated. A "fixed result" is basically one in which multiple calls to either the: Expression.isTrue(Object,Query) or Expression.getValue(Object,Query) methods will return the same object (or that o1.equals (o2) == true) regardless of the object passed to the method.

指定者:

hasFixedResult 在类中 Expression

参数:

q - The Query object.

返回:

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

init

public void init(Query q)
          throws QueryParseException

从类复制的说明: Expression

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

指定者:

init 在类中 Expression

参数:

q - The Query object.

抛出:

QueryParseException - If something goes wrong with the initialisation.

getRight

public ValueExpression getRight()

Get the RHS value expression.

返回:

The RHS.

getLeft

public ValueExpression getLeft()

Get the LHS value expression.

返回:

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.

指定者:

evaluate 在类中 ValueExpression

参数:

o - The object to perform the expression on.

q - The Query object.

返回:

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

抛出:

QueryExecutionException - If an error occurs during processing.

toString

public String toString()

从类复制的说明: Expression

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

指定者:

toString 在类中 Expression

返回:

A string representation of the expression.