I am a student and I hate not knowing how things are organized. I'd like to be able to create a full on java project from scratch on the command line. I'd like to be able to import jars and set the classpath, make packages and import them. ALso learn about environment variables. I currently do not know much about organizing code. I just know how to code in Java.
Is there a textbook, online article or the like that allows one to learn how to organize a java project?
I do not want any involvement with eclipse or any IDE. I am willing to learn Maven, XML, or the likes to accomplish my goal.
If you are a student willing to have a Java programming career, it might help to learn how to do things from command line, e.g. edit the files, compiling the classes, testing and building the project. Oracle tutorials provide example on this matter: https://docs.oracle.com/javase/tutorial/getStarted/cupojava/win32.html#win32-2
However, I strongly advise you to embrace an IDE as your Java career will mostly reside in an IDE as real life projects are BIG! There are tons of helpful things the IDE does to you out of the box or to simplify things. Since you are a student, I will give you one basic example besides compiling: a class with 10 fields requires you some typing for getters, setters, hashCode, equals. Alternative? Few keystrokes to instruct the IDE to generate them for you. And that's one basic example.
Regarding the project structure, embracing the (since you mentioned it) Maven project structure of src/main/{java,resources}, src/test/{java,resources} even if you do NOT use Maven. This will let you forget about organizing the files around.
If you were asking about structuring the classes in the right packages, you will figure out yourself as you gain experience. Rule of thumb is to group classes together by functionality they provide. Additionally, if the packages are organized right, if you change something and touching a few classes, ideally you'd want the changed classes to be located in a single package if possible.
Learning Maven is a good choice as it is a powerful tool for building a project and keeping things organized (project structure, project dependencies, etc.).
A simple Java program can be compiled trivially by javac MyMainClass.java, provided that your CLASSPATH list directories and jars with its dependencies.
Compiling a large Java project is not trivial. There are several tools intended to make it simpler.
Gradle: very widely used, uses its own language, very powerful and complex.
Maven: Still widely used. Uses XML to describe everything.
Apache Ant is lower level and lower abstraction power.
The power of these tools lies exactly in hiding the boilerplate of the Java project building process. They generate a skeleton of a build for you, and provide higher-level operations.
Of course you can start with simplest and watch the steps these tools make.
Reading the docs for javac and jar thoroughly does help, too.
Related
Say I implement an algorithm for a project. Say I want the same code to be used on another project. What would be the approach to do so? Just copy and paste code? Create a "library" project? What? Is there a tutorial or site that explains how to do this?
Sure, add it to a library project, but the benefit of reuse should always be compared to the cost of making the code general. Sure if you improve the code by fixing a bug or increasing performance, it is nice to get that into all projects where you use the code, but it also makes you slower because you have to keep the library compatible with all clients (at least the ones that will build after a breaking change).
It is often better to copy and adapt solutions to new projects, than to maintain far more complex solutions. One very important thing to take into account is how many client you think you will have for the library. How much work would it be to maintain those clients separately?
On the other hand some code is generic by nature and can most definitely be shared in a library to make your life easier.
If your algorithm is in Java, build it as a jar.
Then create a folder called "libs" in the root directory of your android project. Copy your jar into that folder. In eclipse go to
-> Properties -> Java Build Path
Under tab "Libraries", add your jar.
Now you can use your code.
You can as well link it with multiple projects.
If your algorithm is in natice C/C++, follow
http://marakana.com/s/introduction_to_ndk,1153/index.html
If you have a class/set of classes generic enough to be reutilizable, the solution would be separating them to a different project.
In your IDE, make your projects use the generic project as part of their build path (it is more flexible than including a jar).
When deploying, package all the generic classes in a jar and it to your solution. Don't forget to include that jar in the classpath.
In Java, there is no difference between "main project" and "library", other than the "library" usually does not include any main method (but it is not forbidden). They are classes in the classpath.
I got the Java classes from an APK after using some tools like dex2jar and JD-GUI. As everybody knows Java byte code can be converted to Java classes back so mostly it is optimized and obfuscated through some tools (like ProGuard is used in the case of Android) to make it secure from others. So what I got is obfuscated code and I want to make it error-free, readable, understandable so that I can further modify it for my own purpose (for my personal use only, I don't mean to violate any copyrights). So any help i.e advices, tools, helping material to make this obfuscated code much closer to what was written by a developer or to make it error-free and understandable will help me a lot. Currently my focus is about to reversing obfuscating techniques used by ProGuard like when I tried reverse engineering on my own projects and found that:
int resource values can be altered with ids by matching through the R file which is generated with reverse engineering.
The if/else conditions mostly converted to while(true) and some continues and breaks.
Inner classes mostly broke up to separate files
So, any other techniques and helping material for the above mentioned ways which can describe how to properly reverse them will be very helpful.
There isn't a magical tool that will refactor obfuscated code into a buildable project. Most likely, you won't be able to decompile and de-obfuscate an APK to be clean and maintainable code. This is a good thing.
There are tools which are better than dex2jar and jd-gui. One of them is apk-deguard, which claims to reverse the process of obfuscation. From their about page:
DeGuard
DeGuard (http://www.apk-deguard.com) is a novel system for statistical
deobfuscation of Android APKs, developed at the Software Reliability
Lab, ETH Zurich, the same group which developed the widely used JSNice
system. Similarly to JSNice, DeGuard is based on powerful
probabilistic graphical models learned from thousands of open source
programs. Using these models, DeGuard recovers important information
in Android APKs, including method and class names as well as
third-party libraries. DeGuard can reveal string decoders and classes
that handle sensitive data in Android malware.
You should use Enjarify, which is owned by Google, instead of dex2jar. Also, apktool is good for decompiling an APK's resources, which is not handled by dex2jar and enjarify.
Other tools include jadx, procyon, fernflower, show-java, smali/baksmali.
You will need a good IDE for refactoring. JEB looks like a good tool for refactoring. This is a paid tool mostly used by Android security researchers.
This should help:
DeObfuscator
Reverse engineering is a difficult task (i would say subtle art), mostly hit and miss, especially with obfuscated code, what you can do is to focus in some special function, that seems pretty obvious and start from there, renaming and refactoring classes, also a good IDE may help you a lot (my personal recommendation: NetBeans).
I've had several classes - university level - on Java.
However, what these classes lack is some practical approach to Java - or, to programming as a whole. Things you can only learn in a business.
However, since I am not allowed to use Java on the workfloor, I don't get to learn this now - even though I would like to.
So I guess what I'm asking for is any number of plain have-to-know Java resources. Things concering, for example, what Ant is and why and how to use it; using revision control systems from your IDE; standard Java libraries you would use often ... Anything that would help with actual software development, really.
As some side information, I've been using Eclipse for about four years now, and I feel at home there.
I have a system that works fairly well for class assignments and for projects as well. Firstly, I create one Eclipse project per class. This way I can re-use classes from previous assignments. You can also customize your classpath by adding another project as a library.
I use the Maven plugin for Eclipse M2Eclipse. Not only does this give you the ability to search for libraries and add them easily but the exec:java plugin is an easy way to execute your code from the command line. It's helpful because when it executes your code, it uses a classpath that includes all linked Maven dependencies. If you aren't using external libraries, you might not need Maven but I've found it to be helpful to learn in preparation for the job market. It's fairly simple to start with plus there are a ton useful plugins for open source projects.
Next, for revision control I recommend Subclipse. You can get a free SVN account with a single login from Unfuddle.com. Link that up to your Eclipse environment and Import your project.
When I want to get a particular class specification, I go to Sun's Java documentation.
Another excellent resource that will certainly give you the reference material (searchable!) to answer any java question would be this torrent containing ~100 ebooks on Java, sorted by directory on various topics (like Ant, Eclipse, or Swing).
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Can anyone recommend a light Java IDE that doesn't require you to make new projects each time you want to compile and run a program? I just want to be able to open java files and compile and run them. I have already tried Eclipse and NetBeans but both require you to make a new project each time you want to compile and run a program. Making a new project is fine for large scale projects but for small school assignments this just makes the process more tedious.
I've been doing java school assignments using Eclipse. I had one project called "Homework", and created a new package for each assignment. That worked fine for me.
Update: in addition to the practice suggested above, it seems eclipse has a subproject (still in incubation, though) called ide4edu that is specifically for educational purposes.
The Eclipse IDE for Education is a version of Eclipse streamlined specifically for use by university and college students.
In Eclipse, you can just paste code into the package explorer without a given project, and a new project is created containing a file with that code, inside a main method. If the text you paste is a full class, it will name the file according to the class name. You could also set up a single project for your stuff and paste the code or the files you want to run into that project.
I've used Notepad++ to do this for simple Java projects and it worked quite well. Here is a guide on how to do this.
You may also want to check out jEdit, I believe it offers similar functionality, and may be more feature-rich for Java than Notepad++ is.
My school uses DrJava for the first intro to programming class. Its a lightweight IDE and allows you to create folders on the fly for your java classes.
However, my classes now require Eclipse or Netbeans, and it did take some getting used to them. In some places, Eclipse is overkill for a second-year CS student, but I do like its features & am having fun exploring the extensability with other languages.
It might sound geeky or "not for novices" but in order to compile and run a single file the best option(in my opinion) is a console environment.And of course you can view them from notepad++ or any editor with similar fetures(especially highlighting).
How about using a editor like Vim, or Emacs and then install some plugins so that you can have basic IDE features like code completion, etc? You will need to do bit of monkeying to get the right kind of combination and comfort. But, it could well be your answer for a lightweight IDE, one that does not require you to create a project.
NetBeans can have an arbitrary number of classes with main() methods. Create a project named school using NetBeans and create a new package for each group of related assignments. Customize the default configuration menu to make F6 run your current main(). At the same time, develop your skill with bash and a favorite command line editor.
Some universities (like mine) use
BlueJ
for Java Teaching. It basically got everything you need for your homework assignments, and it got NO code completion, which I find perfect for Java beginners ^^.
What's wrong with creating project? Just create it ones and then use it for all your assignments. That will let you use any good IDE (NetBeans, Eclipse, Intellij Idea, ...) which, from other side, greately simplifies writing java code.
I recommend bash. I write a lot of test programs for work (and for the likes of answering stackoverflow questions). javac MyMain.java && java MyMain and you are done.
I have done one project and many unrelated packages, but that sucks. It also cannot cope with more complicated build cases (when dealing with, for instance, serialisation or class loaders).
Personally I enjoy using Emacs for editing my code than then Ant to build / compile my Java code.
Bare in mind that using a lightweight editor will generally mean loosing out on some very useful features, for example:
Auto completion. So for example in Eclipse if you start typing System.out. you can a list of options to complete the statement along with which parameters the function will require
Mistake highlighting : nice "red swiggly lines" highlighting simple mistakes
Build path management : adding external archives is trivial in eclipse less so from the command line for those with little experience
Amongst many others.
Personally I'd way up whether the "faff" of setting up a new project for a simple Java application is worth loosing those really useful features. And that usually varies per task.
I recommend jGRASP. It's a (very) lightweight Java editor, good for the beginning programmer. You can literally paste in some code, compile and save, and your program is ready to be run.
You need a well defined classpath before you can just compile you classes, and that's exactly what the project setup is for.
Just create a project once and forget about it - use it for all your stuff.
you can use cedit. which is not exactly a IDE but you can have compiler and JVM tools attatched to it and you can do whatever you have mentioned. i mean creating a small java file compile and run.
you can that here http://mac.softpedia.com/get/Word-Processing/CEdit.shtml
Why don't you create one project and fill it with all the programs you ever write. There is nothing forcing you to create a new project each time. The only reason to have multiple projects is to make managing the programs easier. So if projects don't make your life easier don't create multiple projects.
BTW: I suggest IntelliJ as I believe it is better, but in this case I suggest the problem is how you work and changing IDE won't make much difference.
This sounds redundant, but the posters are right. However, you know what you can run. If you don't have the resources and you need to run a webserver, putty, etc.. notepad ++ would work (light enough). If your desktop is nice and can handle it, use Eclipse (vast adoption). Create a java project and add packages to it (as Kaleb, Frank and other suggested).
To use IDE for assignment, my approach is to create a test project and use it each time for different assignments. Because in IDE like Netbeans and Eclipse, each class file can be made executable, thus it is quite convenient acutally.
Also for assignments if you want to have more control over your code, Notepad++ is very good for writing codes. You can add in features such as Compile and Run using macros in Notepad and make shortcut key for it.
VIM and Emacs can also be good choices as my friend often talk with me about them. Well i am not quite familiar, you can try it.
I intend to develop a system that is entirely based on modules. The system base should have support for finding out about plugins, starting them up and being able to provide ways for those modules to communicate. Ideally, one should be able to put in new modules and yank out unused modules at will, and modules should be able to use each other's funcionality if it is available.
This system should be used as a basis for simulation systems where a lot of stuff happens in different modules, and other modules might want to do something based on that.
The system I intend to develop is going to be in Java. The way I see it, I intend to have a folder with a subfolder for each module that includes a XML that describes the module with information such as name, maybe which events it might raise, stuff like that. I suppose I might need to write a custom ClassLoader to work this stuff out.
The thing is, I don't know if my idea actually holds any water and, of course, I intend on building a working prototype. However, I never worked on a truly modular system before, and I'm not really sure what is the best way to take on this problem.
Where should I start? Are there common problems and pitfalls that are found while developing this kind of system? How do I make the modules talk with each other while maintaining isolation (i.e, you remove a module and another module that was using it stays sane)? Are there any guides, specifications or articles I can read that could give me some ideas on where to start? It would be better if they were based on Java, but this is not a requirement, as what I'm looking for right now are ideas, not code.
Any feedback is appreciated.
You should definitely look at OSGi. It aims at being the component/plugin mechanism for Java. It allows you to modularize your code (in so-called bundles) and update bundles at runtime. You can also completely hide implementation packages from unwanted access by other bundles, eg. only provide the API.
Eclipse was the first major open-source project to implement and use OSGi, but they didn't fully leverage it (no plugin installations/updates without restarts). If you start from scratch though, it will give you a very good framework for a plugin system.
Apache Felix is a complete open-source implementation (and there are others, such as Eclipse Equinox).
Without getting into great detail, you should be looking at Spring and a familiarization with OSGI or the Eclipse RCP frameworks will also give you some fundamental concepts you will need to keep in mind.
Another option is the ServiceLoader added in Java 1.6.
They are many way to do it but something simple can be by using Reflection. You write in your XML file name of file (that would be a class in reallity). You can than check what type is it and create it back with reflection. The class could have a common Interface that will let you find if the external file/class is really one of your module. Here is some information about Reflexion.
You can also use a precoded framework like this SourceForge onelink text that will give you a first good step to create module/plugin.