it.amattioli.workstate.actions
Class NullGuard

Show UML class diagram

java.lang.Object
  it.amattioli.workstate.actions.AbstractGuard
      it.amattioli.workstate.actions.NullGuard

All Implemented Interfaces:

Guard

public class NullGuard
extends AbstractGuard

A guard whose check(AttributeReader, AttributeReader) method always returns true

Istances of NullGuard are used as null-objects. It is implemented as a singleton so to get an instance use the getInstance() factory method.

Field Summary

static Integer

NULL_GUARD_PRIORITY

Fields inherited from class it.amattioli.workstate.actions.AbstractGuard

USER_PRIORITY

Method Summary

boolean	check(AttributeReader event, AttributeReader state) Check if the condition is satisfied or not.
static NullGuard	getInstance()
Integer	getPriority() Return the priority level for the guard evaluation.

Methods inherited from class it.amattioli.workstate.actions.AbstractGuard

equals, hashCode, toString

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

NULL_GUARD_PRIORITY

public static final Integer NULL_GUARD_PRIORITY

Method Detail

getInstance

public static NullGuard getInstance()

check

public boolean check(AttributeReader event,
                     AttributeReader state)

Description copied from interface: Guard

Check if the condition is satisfied or not. The check can be performed using event parameters and state attributes.

Parameters:

event - the event that triggered the transition to which this guard is associated

state - the state that completely contains the transition to which this guard is associated

getPriority

public Integer getPriority()

Description copied from interface: Guard

Return the priority level for the guard evaluation. To choose the right transition to trigger all the guards must be evaluated to know which is true. Normally all the guards should be indipendent one each other and the evaluation order should not be important. But to implement an "else" mechanism a priority has been associated to the guards. The null guard has a very low priority while all user defined guards have a high priority. In this way the null guard is always evaluated as the last guard and, as it always returns true, it works like an "else" branch. The priority should not be used for other purposes like forcing the evaluation order of user defined guards.

Specified by:

getPriority in interface Guard

Overrides:

getPriority in class AbstractGuard