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The goal of this project is to convert a simple Java stopwatch to an Android application. The original java code can be found here.

Learning Objectives


  • Modeling state-dependent behavior with state machine diagrams (see also here)
  • Distinguishing between view states and (behavioral) model states


  • Event-driven/asynchronous program execution
  • User-triggered input events
  • Internal events from background timers
  • Concurrency issues: single-thread rule of accessing/updating the view in the GUI thread

Architecture and Design

  • Key architectural issues and patterns
    • Simple dependency injection (DI)
    • Model-view-adapter (MVA) architectural pattern
    • Mapping MVA to Android
    • Difference between MVA and model-view-controller (MVC)
    • Distinguishing among dumb, reactive, and autonomous model components
  • Key design patterns
    • Implementing event-driven behavior using the Observer pattern
    • Implementing state-dependent behavior using the State pattern
    • Command pattern for representing tasks as objects
    • Façade pattern for hiding complexity in the model from the adapter
  • Relevant class-level design principles
    • Dependency Inversion Principle (DIP)
    • Single Responsibility Principle (SRP)
    • Interface Segregation Principle (ISP)
  • Package-level architecture and relevant principles
    • Dependency graph (see also here)
    • Stable Dependencies Principle (SDP)
    • Acyclic Dependencies Principle (ADP)
  • Architectural journey


  • Different types of testing
    • Component-level unit testing
    • System testing
    • Instrumentation testing
  • Mock-based testing
  • Testcase Superclass pattern (uses Template Method pattern)
  • Test coverage

Setting up the Environment

Check out the project using Android Studio. This creates the file with the required line

sdk.dir=<root folder of Android Studio's Android SDK installation>

Running the Application

In Android Studio: Run > Run app

Running the Tests

Unit tests including out-of-emulator system tests using Robolectric

In Android Studio:

  • Before running tests, in the Android view right-click on edu.luc.etl.cs313...test (test) - if Select ... is one
  • of the visible menu items about 2/3 of the way down, click on that; if Select ... is not there, go to the next step
  • Now click Run > Edit Configurations... and under Android JUnit click on cs313 in app
  • On the Configuration tab, click the far-right icon in the Working Directory row and select MODULE_DIR, then click OK
  • If you do not do this, running the unit tests from the Android view will not work!
  • Finally, right-click on edu.luc.etl.cs313...test (test), then choose Run 'Tests in 'test''

You can also use Gradle:

$ ./gradlew testDebug # leave out the "./" on the Windows command line

You can view the resulting test reports in HTML by opening this file in your browser:


Unit test code coverage

In Gradle:

$ ./gradlew jacocoTestDebugUnitTestReport # leave out "./" on the Windows command line

You can view the resulting test reports in HTML by opening this file in your browser:


Android instrumentation tests (in-emulator/device system tests)

In Android Studio:

  • In the Android view, right-click on (androidTest), then choose Run 'Tests in ''

You can also use Gradle:

$ ./gradlew connectedDebugAndroidTest # leave out "./" on the Windows command line