We Keep Coding

Eclipse: sharing package between two projects for testing

The problem is that I use Mockito for testing a class with some protected methods. In order to mock them I need my tests to be in the same package.
I'm using the following scheme now:
project
---src
------some.package.for.class
---------MyClass.java
---tests //source folder
------some.package.for.class //so test package looks the same
---------Tests.java
It works, but the problem is that I don't trylly understand how. As I understand, BuildPath is part of Eclipse IDE, which help Eclipse to find files and libraries for my project.
So how is it possible to keep tests in other folder but in the same package???
And another question: is it possible to keep java files in one packages, yet in different projects?

Is it possible to have class files in the same package but in different folders? Yes.
Is it possible to have class files in the same package but in different projects? Yes.
When the classes load, they can come from many different places, including different JARs, but still be in the same package.
Regarding Eclipse, you just need to make sure you've selected all the source folders (including tests) in Java Build Path > Source. There is no restriction that says all class files in the same package must be in the same folder.

It's best to use the maven conventions for source files
(Gradle adheres to many maven conventions too).
Therefore, I'd use:
src/main/java/some/package/for/class/MyClass.java
src/test/java/some/package/for/class/MyClassTest.java

Referencing wrong jar file in java build-path

In my project we are referencing lot of dependency .jar files.
/lib/xxx.jar
/lib/abc.jar
The xxx.jar file having some (com.search.hit) packages. The same packages are available in abc.jar file.But the problem comes into picture now, where accessing xxx.jar file it doesn't referencing their package(com.search.hit) instead it is referencing abc.jar package.
Could anyone tell how to redirect the flow?

The class from whichever jar comes first on the classpath is the one that is used. The other one might not even exist as far as the classloader is concerned. It's a good idea to avoid conflicts like this.

In Eclipse go to your project build path configuration and click on the Libraries tab.
Then remove the package that you don't want to be accessed from your list and add it again.
This will cause the package to be lower in the priority list and it'll check the other package before the one you just re-added.

This will create problems for you. My suggestion would be to create 2 extra classes for writing getter and setter wrappers for these jar files. Write 2 seperate classes, each one of them will reference just one of them and your project file will use these wrapper classes to invoke functions from these jars. It would be a lot easier that way.

You have to change the package name it can not be same file name with same package in single JVM. JVM will take load randomly one jar class using class loader and ignore the rest.

In Java, should I be creating a new Package, Folder, or Source Folder?

There are a couple of questions on SO that sort of hit this, but I am totally new to Java development and I don't know the correct way to approach this.
I have a C# solution, containing two projects (my app, and a unit test project) and within the app, most things are put into folders eg. Interfaces, Exceptions etc.
I am trying to recreate this in Java / Eclipse, but I don't know how. I ended up with lots of packages, which sounds really bad. I also tried adding a source folder but that ended up being outside of the package.
Could anyone point me in the right direction?
Namely, which of those should I use to represent my unit test project/set of unit tests, and subfolders which exist just for organising stuff.
Edit: It also says use of the default package is not advised. What should I be doing?
Edit 2: Here is what it looks like. Does this look vaguely correct? My original C# solution is on the right.

In a typical java eclipse project, you will have one or more source folders (for example one for app code, one for your unit tests).
Each folder contains a package tree, typically starting with your base package, for example com.mycompany.myapp.
In order to avoid name collisions, packages names are usually start with the domain name of the entity who is the author of the code, starting with the top-level-domain and going backwards (more general to more specific). That way, each class fully qualified name is unique. For example if google creates a class named List, it will be known as com.google.List, and it will not enter in conflict with the existing java.util.List interface.
You can have a unlimited number of packages inside this base package, for example :
com.mycompany.myapp.persistence
com.mycompany.myapp.domain
com.mycompany.myapp.services
com.mycompany.myapp.web
It all depends on your project and the way you want to organize your code and your classes.
At the logical level, packages are named with dots as separator. They contain java classes.
At the physical on disk level, each package is a directory. The java classes are contained in .java files (most frequently one class per file).
In Eclipse a "source folder" is a folder inside your project that is known to Eclipse to contain java source files. It will be compiled included in the output (for example JAR file) when you build your project.
In Eclipse, you usually view them at the logical level, showing packages. When you tell Eclipse to "create a new package", it will create the directory for you. For example, if you tell it to create the com.mycompany.myproject package, it will automatically create a com folder containing a mycompany folder containing a myproject folder.

In java source tree structure must match package structure
so foo.bar package must be laid out in
src/foo/bar
Also default package may not be advised - but you can still use it - better to put things in a package though

In java different project development structure are flowed according to type of project.
So as you are new to java and Eclipse so it's better to install maven plugin and create maven project and choose a archetypes according to your project type like a standalone or web based.
The maven plugin will create the project structure including packages,test packages source folder etc. You can get more about project structure from this

Using the default package may create namespace collisions. Imagine you're creating a library which contains a MyClass class. Someone uses your library in his project and also has a MyClass class in his default package. What should the compiler do? Package in Java is actually a namespace which fully identifies your project. So it's important to not use the default package in the real world projects.

Import classes from folder

I am new to android and i want to import some classes to my application wich are placed in MyClasses folder in same package.
After googling for a time I found a way to do this by usig Java build path and in this add class folder. I think this may solve my problem but no luck.
I don't know how to import classes from folders. Is it possible to import classes from folder? If it is possible then how to do this?
Any help will be appreciated.

I assume this is for Eclipse. You have the options for importing a Class Folder, which is not very useful in my opinion since it only loads folders in projects you have defined in your workspace. In this scenario I would just link to the project itself. But you can also import External Class Folders. If this is what you are trying to accomplish then make sure you are using the correct item in the Java Build Path dialog.

The problem that Dalvik does not understand java files. They should be compiled into the internal Dalvik format dex. And even after that I'm not sure that you can dynamically load files into your project.

Have the folder in your build path, then use:
Class.forName("package.className")
It will also call the static constructor for the classes loaded this way (this pattern is used with JDBC drivers).
If you want to change the folder at runtime, you might have to write your own class loader.
This might help more: http://www.techrepublic.com/article/get-the-most-out-of-javas-class-loaders/6080883
Not sure how this works with Android, though. I don't think you can implement your own class loader for Android due to security issues.

Change the package of a JAR from the default package

I've downloaded a JAR file from my teacher's website containing some classes in the default package, and I'm thus unable to access them from inside a defined package.
I have read that the preferable solution is to repackage the JAR, changing the package name. However I have no idea how to go at it. The solution probably involves using Ant or Jar Jar, but I've no experience with either tool. I would love if someone coould point me in the right direction.
Thanks.

You need to change the sources and recompile then to change the package - simply moving the class files inside the jar (or outside) does not help.
So ask your teacher to give you the sources (or to put the classes in a suitable package), or use a decompiler to do this yourself.

You can unjar/unzip them manually, create the package and jar them back using and IDE or from the command prompt like this. Also, take a look at the ANT documentation on Jar and Unjar which is quite comprehensive.

As #Piyush Instructed use the below command for creating a Jar file.
jar -cvf *.* Example.jar

If you are using eclipse, just unjar the source files into the source folder of a temporary project. Then, create a new project (the real project you will be working on), and under the java/src directory, create the package structure you want. Then it's just a simple matter of drag-n-dropping the source files from the temporary project into the correct packages in the real project. Eclipse will take care of changing the package declaration of each class for you.