Standard Java and Android library usage

You can use Java classes that are part of the standard Java library and Android™ Java library.

Using standard Java within the GMA

Java classes provided in the standard Java library and in the Android Java library can be used directly by including the IMPORT JAVA classname keywords in the Genero code:

IMPORT JAVA java.lang.Runtime
IMPORT JAVA android.os.Build

MAIN
  DEFINE rtm Runtime, msg STRING

  LET rtm = java.lang.Runtime.getRuntime()

  LET msg = SFMT("Device:[%1] %2 - %3 (%4 procs)",
                 android.os.Build.MANUFACTURER,
                 android.os.Build.MODEL,
                 android.os.Build.SERIAL,
                 rtm.availableProcessors() )

  MENU "Test" ATTRIBUTES(STYLE="dialog", COMMENT=msg)
    ON ACTION ok
      EXIT MENU
  END MENU

END MAIN

The Android Java library does not include all the classes of a regular JRE. User interface classes are specific to the Android user interface framework. The list of standard Android Java packages can be found at http://developer.android.com/reference/packages.html.

Only non-interactive classes can be used in this context. To get a graphical user interface, you must implement an Android Activity, as described in Implement Android activities in GMA.

Because Android apps are Java-based, the JVM and standard Java library is directly available. There is no need to bundle the Java library with your Genero program files when you deploy your app as .apk package.

When executing the Genero program on a computer in development mode, it is not possible to use classes that are specific to the Android Java library, because the Android Java library is not available in development mode at runtime.

You must compile your app code and deploy it on an Android device for execution. To compile your app code on the development platform, you need to setup the Java SDK environment and the CLASSPATH to the Android SDK library (android.jar).

JVM context-dependent Android API calls

On an Android device, the GMA executes a Genero program in a JVM process. Some Android system APIs cannot be directly called from the Genero runtime system context; they must be called from the JVM context.

In order to call such APIs, you must import the com.fourjs.gma.vm.FglRun class and get the Android JVM thread context by calling the getContext() method of the FglRun class.

The getContext() method will return an instance of the android.content.Context class. For more details, see http://developer.android.com/reference/android/content/Context.html

To use this Android JVM interface, you must add the android.jar library (from the Android SDK) to the class path.

The com.fourjs.gma.vm.FglRun class implements the following methods:

Table 1. Methods of the com.fourjs.gma.vm.FglRun class
Method	Description
`Context getContext()`	Returns the Android JVM context object of the runtime system.

In the program code, use the getContext() method to get the JVM context and call specific Android APIs:

IMPORT JAVA android.app.Service
IMPORT JAVA android.content.Context
IMPORT JAVA android.util.DisplayMetrics
IMPORT JAVA android.view.WindowManager

IMPORT JAVA com.fourjs.gma.vm.FglRun

MAIN
    DEFINE w, h, d INT
    MENU "Java"
       ON ACTION test
          CALL android_screen_metrics() RETURNING w, h, d
          MESSAGE "Width: ", w, "\nHeight: ", h, "\nDensity: ", d
    END MENU
END MAIN

FUNCTION android_screen_metrics()
    DEFINE ctx android.content.Context,
           dm android.util.DisplayMetrics,
           wm android.view.WindowManager

    LET ctx = com.fourjs.gma.vm.FglRun.getContext()
    LET dm = android.util.DisplayMetrics.create()
    LET wm = CAST ( ctx.getSystemService("window")
                    AS android.view.WindowManager )
    CALL wm.getDefaultDisplay().getMetrics(dm)

    RETURN dm.widthPixels,
           dm.heightPixels,
           dm.densityDpi
END FUNCTION

Using front calls instead of pure Java

For maximum portability, consider implementing Android-specific extensions as custom front calls. When using the front call technology, apps can be executed in development (app running on the server) and in deployed mode (app running on the mobile device) with the same Genero code.

For more details about custom front calls with GMA, see Implement front call modules for GMA.