I am trying to build an app which is composed out of separate library projects.
To do this, I'm trying to make a proof of concept which is supposed to be as following:

I tried to keep the project as simple as possible. The projects contents do not matter!
All that matters is the dependencies between the projects!
The result should be that MainProject will print out Something Another String!
I have tried all from .JAR files to .AAR files, but the best I got was
with the dependency in red. I added the StringExtender.aar file to StringReturner, and then the StringReturner.aar file to the MainProject.
When I do this I get the following Exception:
java.lang.NoClassDefFoundError: Failed resolution of: Lcom/example/erik/stringextender/StringExtender;
What is the right way to setup a simple proof of concept like this? I can't seem to find anything related to a library project having a dependency. It's all 1 level deep!
Any help is welcome!
EDIT SHOWING GRADLE BUILD FILES
StringReturner:
apply plugin: 'com.android.library' android { compileSdkVersion 23 buildToolsVersion "23.0.3" defaultConfig { minSdkVersion 15 targetSdkVersion 23 versionCode 1 versionName "1.0" } buildTypes { release { minifyEnabled false proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro' } } } dependencies { compile fileTree(include: ['*.jar'], dir: 'libs') testCompile 'junit:junit:4.12' compile 'com.android.support:appcompat-v7:23.2.1' compile project(':StringExtender-lib-debug') } MainProject:
apply plugin: 'com.android.application' android { compileSdkVersion 23 buildToolsVersion "23.0.3" defaultConfig { applicationId "com.example.erik.erikpoc10" minSdkVersion 15 targetSdkVersion 23 versionCode 1 versionName "1.0" } buildTypes { release { minifyEnabled false proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro' } } } dependencies { compile fileTree(include: ['*.jar'], dir: 'libs') testCompile 'junit:junit:4.12' compile 'com.android.support:appcompat-v7:23.2.1' compile 'com.android.support:design:23.2.1' compile project(':StringReturnerLib-debug') }