Active object: Difference between revisions

[[Category:Object oriented]]

 

In [[object-oriented programming]] an object is active when its state depends on clock. Usually an active object encapsulates a [[task]] that updates the object's state. To the outer world the object looks like a normal object with methods that can be called from outside. Implementation of such methods must have a certain synchronization mechanism with the encapsulated task in order to prevent object's state corruption.

A typical instance of an active object is an animation widget. The widget state changes with the time, while as an object it has all properties of a normal widget.

 

Implement an active integrator object. The object has an input and output. The input can be set using the method ''Input''. The input is a function of time. The output can be queried using the method ''Output''. The object integrates its input over the time and the result becomes the object's output. So if the input is ''K''(''t'') and the output is ''S'', the object state ''S'' is changed to ''S'' + (''K''(''t''₁) + ''K''(''t''₀)) * (''t''₁ - ''t''₀) / 2, i.e. it integrates ''K'' using the trapeze method. Initially ''K'' is constant 0 and ''S'' is 0.

 

In order to test the object:

# wait 2s

# set the input to constant 0

# wait 0.5s

 

 

=={{header|Ada}}==

with Ada.Numerics; use Ada.Numerics;

with Ada.Numerics.Elementary_Functions; use Ada.Numerics.Elementary_Functions;

Put_Line ("Integrated" & Float'Image (S) & "s");

I.Shut_Down;

Sample output:

<pre>

</pre>

 

 

 

#include <stdlib.h>

#include <unistd.h>

#include <math.h>

#include <pthread.h>

 

{

}

 

{

}

 

 

{

{

}

}

 

{

}

 

{

}

 

{

}

 

{

}

}

 

 

int main()

{

 

 

 

<pre>

</pre>

 

 

=={{header|E}}==

 

 

 

=={{header|JavaScript}}==

{{trans|E}}

 

var inputF = function () { return 0.0 };

var sum = 0.0;

shutdown: function () { clearInterval(updater) },

});

 

Test program as a HTML fragment:

 

 

<script type="text/javascript">

}, 2000);

}, 1)

 

=={{header|Tcl}}==

 

This implementation Tcl 8.6 for object support (for the active integrator object) and coroutine support (for the controller task). It could be rewritten to only use 8.5 plus the TclOO library.

oo::class create integrator {

variable e sum delay tBase t0 k0 aid

pause 0.5

puts [format %.15f [i output]]

Sample output:

-0.000000168952702

 

=={{header|Visual Basic .NET}}==

Since this object is CPU intensive, shutting it down when done is crucial. To facilitate this, the IDisposable pattern was used.

 

Sub Main()

End Sub

Implements IDisposable

End Sub

 

 

Output: 0.000241446762282308

 

 

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