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Jadex Rules is a small lightweight rule engine, which currently
employs the well-known Rete algorithm for highly efficient rule
matching. Jadex rules is therefore similar to other rule engines
like JESS and Drools. Despite the similarities there are also
important differences between these systems:
* Jadex Rules is very small and
intended to be used as component
of other software. Even though rules can be specified in a Java
dialect as well as (a small variation of) the CLIPS language
its primary usage is on the API level. Jadex Rules is currently
the core component of the Jadex BDI reasoning engine.
* Jadex Rules cleanly separates between state and rule representation.
This allows the state implementation as well as the matcher to be
flexibly exchanged. Some experiments have e.g. been conducted with
a Jena representation. Regarding the matcher, it is planned to
support also the Treat algorithm, which has a lower memory footprint
than Rete.
* Jadex Rules pays close attention to rule debugging. The state as
well as the rete engine can be observed at runtime. The rule debugger
provides functionalities to execute a rule program stepwise and also
use rule breakpoints to stop the execution at those points.
package jadex.rules.parser.conditions.javagrammar;
import jadex.rules.rulesystem.rete.extractors.AttributeSet;
import jadex.rules.rulesystem.rules.ILazyValue;
import jadex.rules.rulesystem.rules.Variable;
import jadex.rules.rulesystem.rules.functions.IFunction;
import jadex.rules.state.IOAVState;
/**
* A conditional operation uses a condition to choose from two values:
* condition ? first_value : second_value
*/
public class ConditionalExpression extends Expression
{
//-------- constants --------
/** A function to evaluate conditionals. */
public static final IFunction FUNCTION_CONDITIONAL = new IFunction()
{
public AttributeSet getRelevantAttributes()
{
return AttributeSet.EMPTY_ATTRIBUTESET;
}
public Class getReturnType()
{
// Todo: get most specific return type of params 1 and 2!?
return Object.class;
}
public Object invoke(Object[] paramvalues, IOAVState state)
{
if(paramvalues==null || paramvalues.length!=3)
throw new IllegalArgumentException("Conditional requires three parameters.");
return ((Boolean)(paramvalues[0] instanceof ILazyValue? ((ILazyValue)(paramvalues[0])).getValue(): paramvalues[0])).booleanValue()
? (paramvalues[1] instanceof ILazyValue? ((ILazyValue)(paramvalues[1])).getValue(): paramvalues[1]):
paramvalues[2] instanceof ILazyValue? ((ILazyValue)(paramvalues[2])).getValue(): paramvalues[2];
}
public String toString()
{
return "?:";
}
};
//-------- attributes --------
/** The condition. */
protected Expression condition;
/** The first value expression. */
protected Expression first;
/** The second value expression. */
protected Expression second;
//-------- constructors --------
/**
* Create a new operation.
*/
public ConditionalExpression(Expression condition, Expression first, Expression second)
{
this.condition = condition;
this.first = first;
this.second = second;
}
//-------- methods --------
/**
* Test if a variable is contained in the expression.
* @param var The variable.
* @return True, when the variable is contained.
*/
public boolean containsVariable(Variable var)
{
return condition.containsVariable(var)
|| first.containsVariable(var)
|| second.containsVariable(var);
}
/**
* Get the condition.
*/
public Expression getCondition()
{
return this.condition;
}
/**
* Get the first value.
*/
public Expression getFirstValue()
{
return this.first;
}
/**
* Get the second value.
*/
public Expression getSecondValue()
{
return this.second;
}
/**
* Get a string representation of this constraint.
*/
public String toString()
{
StringBuffer ret = new StringBuffer();
ret.append(getCondition().toString());
ret.append(" ? ");
ret.append(getFirstValue().toString());
ret.append(" : ");
ret.append(getSecondValue().toString());
return ret.toString();
}
/**
* Test if this constraint is equal to some object.
*/
public boolean equals(Object o)
{
return o instanceof ConditionalExpression
&& ((ConditionalExpression)o).getCondition().equals(getCondition())
&& ((ConditionalExpression)o).getFirstValue().equals(getFirstValue())
&& ((ConditionalExpression)o).getSecondValue().equals(getSecondValue());
}
/**
* Get the hash code of this field access.
*/
public int hashCode()
{
int ret = 31 + getCondition().hashCode();
ret = 31*ret + getFirstValue().hashCode();
ret = 31*ret + getSecondValue().hashCode();
return ret;
}
}