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Server implementation in Java Implementation barcode pdf417 in Java Server implementation




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20.5 Server implementation using barcode generating for jvm control to generate, create pdf-417 2d barcode image in jvm applications. barcode pdf417 the problem improved. Such n barcode pdf417 for Java ame changes are common during OOAD and should not be eschewed. The proper and sensible naming of objects and operations is important for a clear understanding of a design.

) When the client calls initializeSimulation(), the server performs sequence 3, which initializes the SimulationThread with the input data:. public void initializeSimulation (float[] indata) throws RemoteException fSimulationThread.initialize j2ee pdf417 2d barcode (indata);. 20.5.1.

4 The Server.start() method Finally the client calls the server s start() method in order to start the simulation running. This call is forwarded immediately to SimulationThread s start() method at sequence 4 in the collaboration diagram.

. public void start() throws R barcode pdf417 for Java emoteException { fSimulationThread.start();. As usual, calling a thread s start() method invokes the run() method, which we show later. 20.5.

1.5 The retrieveData() method As the simulation runs, simulation data is repeatedly loaded into the SimData object as shown in sequence numbers 4.2.

1 and 4.2.1.

1. We explain those details shortly. For now, we assume that the client periodically polls the server for current simulation data.

The client does so by calling retrieveData(), which simply obtains and returns the latest available data from SimData using its (yet to be discussed) getResults() method (shown as sequence 5 in the collaboration diagram of Figure 20.1):. public float[] retrieveData (float[] indata) throws RemoteException return fSimData.getResults ( indata);. Here we have made the simpli PDF417 for Java fying assumption that the set of data to be returned is a simple float[] array. More complicated structured data could be returned in a Java object with minor modi cations. We have also taken the opportunity to allow the client to provide a new set of input data during each retrieveData() poll.

If the input data has not changed, then the original indata array can be passed each time.. Distributed computing putting it all together As mentioned earlier, for th Java PDF417 is example we are also using the simple technique of returning only the most recent data stored in SimData, allowing any intervening data generated by the computation to be lost if the client does not poll often enough. More elaborate schemes can be devised, such as storing intermediate data in SimData and returning a collection of results, but doing so now would distract from the basic client/server design being demonstrated here..

20.5.2 The SimulationThread class Continuing around the collab PDF-417 2d barcode for Java oration diagram in a clockwise direction, which is roughly the order in which the ojects are encountered, the next class to discuss is the SimulationThread class. It is a thread so it extends java. lang.

Thread:. public class SimulationThrea d extends Thread { . . .

}. When SimulationThread is con pdf417 for Java structed (at sequence 2 in the collaboration diagram), we see that sequence 2.1 also must be performed to construct a Simulation object. So the SimulationThread constructor looks like:.

public SimulationThread (Sim Data sim-data) { fSimulation = new Simulation (sim-data);. where we have passed the Sim jsp pdf417 Data object on to the Simulation constructor as shown in the collaboration diagram. This thread s run() method starts the simulation running by calling the startRunning() method on the Simulation object. We can note from the collaboration diagram that startRunning() is a synchronous call.

That is, it blocks until the calculation is complete, at which time run() exits.. public void run () { fSimula tion.startRunning ();. Recall that the best and pro PDF 417 for Java per way to end a thread is to set a boolean value that the running thread checks periodically. In this case, our run() method is not in a loop itself, but has called Simulation.startRunning() instead.

If the server ever needs to halt the simulation, perhaps on command from the client (through additional remote methods that we do not show here), it is a good idea to provide a halt() method that passes the halt command on to Simulation:. void halt () { fSimulation.h alt ();. 20.5 Server implementation 20.5.3 The Simulation class The computational work is do jvm PDF417 ne in the Simulation class. The constructor does nothing except store a reference to the SimData object:. public Simulation (SimData s d) { fSimData = sd;. The initialize() method is c Java PDF-417 2d barcode alled in sequence 3.1 after the client has called Server.initializeSimulation().

Recall that initializeSimulation() is used by the client to provide initial conditions to the simulation. In our case, we receive a float[] array of values. Each element in the array represents a known physical quantity initial amplitude, spring constant, etc.

Both the client and server must agree upon the proper order of values in the array or else the calculation will be incorrect. A less error-prone technique is to de ne a data-only class, perhaps named SpringParameters with named elds for each desired parameter:. class SpringParameters { flo at amplitude; float springConstant;. ...

}. This class would best appear in the javatech.all20.server package where the interfaces appear, giving it visibility to both the client and server.

The client would instantiate the class, populate each element, and pass it to the server during initializeSimulation(). (If you have read 19, then this class will be familiar since it essentially mimics the role played by a CORBA struct.) Since RMI is adept at moving objects across the network, such a technique would be entirely satisfactory.

We have chosen not to do that here because reading data from a float array is slightly faster than dereferencing an object. For initialization, the speed difference is negligible, but when the client starts polling the server for data updates and providing new input data with each poll, then performance becomes more important. In a complex simulation, the input array could be substantially larger than the example here.

There must be a close coupling between the client and server anyway the server is computing a known simulation on behalf of the client, after all so it s not much of a burden to require that the client and server agree on the order of elements in the array, at the slight cost of increased risk of error. Therefore, instead of a SpringParameters object, we receive a simple float[] array. Let s now decide on the order of elements.

We certainly need the amplitude A, spring constant K, and mass m. From K and m we can calculate the frequency . However, it is more convenient to specify A, K, and and.

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