Eclipse. Run two different mains when the second reads a static field of the previous

Question

I have a Java project in eclipse which is divided in two parts; two different main classes that run two different Threads basically. One contains loading, initialization and debug-showing procedures that are quite slow. While, the other manipulates the initialized data. In order to retrieve the information in the second part, the first one "saves" all the references inside a static map which contains instances of classes.

Does exist a way to run the first part only once, and then compile and run the second part more times? I tried with just set two different console and pressing the run button in different times but the static field of the first class looks not existing when the second runs.

I am working now only in the second part, so I need to test and start it many times. I really appreciate an help to save a lot of time wasted in always initialize the same thing.

ps : Everything works fine if I run both parts together. thanks in advance Luca

thanks to the replay (Multithreader, Stephen C) I am trying to make the question more clear and to ask how to solve it since my solution does not look the best one.....

EDIT 1 : The "first part" initializes the program and then runs an easy GUI which is periodically update. So as long as it shows up we shouldn’t care about how to manage input and output from the user

EDIT 2 : the "second part" reads information from the previous and send back strings to the GUI for debug purposes.

EDIT 3 : I do not have specific constrains in the shape of the project, so I can change the structure if there are better solutions. As well as for the way to run it.

FARTHER QUESTION 1 : there is a possibility to compile only one part of the project in eclipse while it runs all together? I mean, if two threads are running, can I stop one, re-compile it and run it again in a way that it can see the instances created from the first thread which never stops? Basically I need to refer at the same static variable loaded in memory, if it exists.

FARTHER QUESTION 2 : or more luckily does exist a way to store and load in a file instances of Java classes avoiding to write from sketch a mapping mechanism from/into txt files?

Answer 1

I guess I found a tricky solution. It is dirty but it works natively in the eclipse debugger.

I am running in debugging mode a main method which create a thread that works as a caller. This runs the first part of the project and wait until the initialization is complete (note that the first part doesn't end here, it remains looping to show debugging information based on a static class which evolves with the second part of the program). Then it starts with an infinite loop where it just calls the second part that I want to test and change: here there are also a breakpoint. Well, now I can coding in the second parts while the eclipse debugger is waiting in the breakpoint than save it and hit F8. The debugger resumes, the algorithms runs and then it stops again in the breakpoint. Just check if works, eventually change something then save and hit F8 again without wait to re-initialize the first part of the project.

Probably this method has to be restarted after a while but still, it better then restart every time :) many thanks to all your help. If somebody has more elegant way to do that they are welcome!!

Answer 2

It is not entirely clear what you are asking here, but I'm assuming that you are talking about running the "first part" and the "second part" in the same JVM ...

Yes, it is possible. But it is not straightforward.

Basically, you need to refactor your code so that there is some kind of "control box" that the user can interact with from the outside. For instance, this might just be a simple command loop that reads commands from standard input and runs them. (Alternatively you could turn your application into a "service" that accepts requests over a network socket, via RMI, via HTTP, etcetera.)

Then you wire things up so that there is a "command" to run the "second part" of your application in response to the user's request.

That's the basics. The other thing you want to do is to "compile and run the second part [many] times". That implies that you need to set up your "control box" so that it can load a fresh copy of the code for the "second part" after you have modified and recompiled it. To achieve this, you will need to create a new ClassLoader object (each time) and use that to load the classes that make up the "second part". This is possible, but a bit tricky. The problems you are going to need to address include:

• Splitting the "first part" and the "second part" into separate JAR files (or directory trees). The "first part" needs to be self-contained ... no dependencies on classes in the "second part".

• Make sure that there are no runtime references from the "first part" data structures to instances of objects / enums in the "second part".

If you don't get the above right, you are likely to experience "permgen" storage leaks and mysterious type cast errors.

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All in all, there's a lot that needs to be done to make this work. Unless you already understand all of the technologies involved, I'm doubtful that it will save you time overall. A better idea might be to figure out how to speed up the initialization of the "first part"; e.g. by doing lazy initialization, or caching the data structures using some fast / light-weight persistence mechanism.

Answer 3

I think it is better to change your design unless there is a requirement for it to stay the same.

Although I do not have the requirements or what you are actually trying to accomplish, I suggest you the following design: 1. App_1 does the calculations and then writes the results into file 2. App_2 reads checks for the file, if NOT exists display error message; otherwise read the file and keep going...