monq.jfa.actions

Class Call

java.lang.Object

monq.jfa.AbstractFaAction

monq.jfa.actions.Call

All Implemented Interfaces:

java.io.Serializable, FaAction

public class Call
extends AbstractFaAction

is an FaAction that forwards the callback to its invoke() method to a named method by using reflection.

Creating a Dfa with many different callbacks (FaActions) can be tedious, because each action must be in its own class. Although anonymous classes help to reduce the code clutter, the actions often must communicate through a common state. Doing so in a way that the Dfa can be used in parallel threads requires each action to retrieve the common state from DfaRun.clientData and cast it to the type it is known to be — tedious again.

The Call action helps to get rid of the tedious steps described above. Instead of one class per action, just write one class, say Worker, and implement each action as a method. The name of the actions does not matter, they just have to be public and must have the same signature as FaAction.invoke(java.lang.StringBuilder, int, monq.jfa.DfaRun). To use the resulting Worker in a Dfa, two things need to be done:

1. Use Call objects with the action methods' names when creating the Nfa.
2. Provide a fresh instance of Worker in the DfaRun.clientData field of the DfaRun object that operates the Dfa compiled from the Nfa.

When called, the invoke() method of a Call object will retrieve the Worker from the clientData field of its third parameter. Then it uses reflection to find the action to call according to the name specified in the constructor of the Call object.

Example:

public class Worker {
   public void invokeOne(StringBuilder sb, int start, DfaRun r) {
     ...
   }
   public void invokeTwo(StringBuilder sb, int start, DfaRun r) {
     ...
   }
 }

 // somewhere else create the Dfa and the DfaRun
 Dfa dfa = new Nfa("myRe1", new Call("invokeOne"))
               .or("myRe2", new Call("invokeTwo"))
               ...
 DfaRun run = new DfaRun(dfa);
 run.clientData = new Worker();
 ...

Note: I would be interested to hear opinions or measurements whether this approach, using reflection, is slower than using one class per action.

Author:

© 2003-2007 Harald Kirsch

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
Call(java.lang.String methodName) creates a Call that will forward the call to a method with the given methodName.

Method Summary

Modifier and Type	Method and Description
boolean	equals(java.lang.Object _o) returns true if and only if _o is a Call object and invokes the same method name.
java.lang.String	getMethodName() returns the method name specified in the constructor.
int	hashCode()
void	invoke(java.lang.StringBuilder out, int start, DfaRun run) calls the method specified in the constructor by finding it in run.clientData via reflection.

Methods inherited from class monq.jfa.AbstractFaAction

mergeWith, setPriority

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Call

public Call(java.lang.String methodName)

creates a Call that will forward the call to a method with the given methodName.

Method Detail

invoke

public void invoke(java.lang.StringBuilder out,
                   int start,
                   DfaRun run)
            throws CallbackException

calls the method specified in the constructor by finding it in run.clientData via reflection.

Throws:

CallbackException - if the method called throws it. In that case the exception is rethrown.

java.lang.IllegalArgumentException - if the named method cannot be found in run.clientData, if the invocation results in an IllegalAccessException or if the method called throws a checked exception other than a CallbackException.

getMethodName

public java.lang.String getMethodName()

returns the method name specified in the constructor.

equals

public boolean equals(java.lang.Object _o)

returns true if and only if _o is a Call object and invokes the same method name.

Overrides:

equals in class java.lang.Object

hashCode

public int hashCode()

Overrides:

hashCode in class java.lang.Object