Libgdx employs its own logging facility. You can choose a log level to filter what should be printed to the platform's console. The default log level is LOG_INFO. You can use a settings file and/or change the log level dynamically at runtime using the following code line:

Gdx.app.setLogLevel(Application.LOG_DEBUG);

The available log levels are:

To write an info, debug, or an error log to the console, use the following listings:

Gdx.app.log("MyDemoTag", "This is an info log.");
Gdx.app.debug("MyDemoTag", "This is a debug log.");
Gdx.app.error("MyDemoTag", "This is an error log.");

You can tell Libgdx to shutdown the running application. The framework will then stop the execution in the correct order as soon as possible and completely de-allocate any memory that is still in use, freeing both Java and the native heap. Use the following listing to initiate a graceful shutdown of your application:

Gdx.app.exit();

If you want to persist your data, you should use the Preferences class. It is merely a dictionary or a hash map data type which stores multiple key-value pairs in a file. Libgdx will create a new preferences file on the fly if it does not exist yet. You can have several preference files using unique names in order to split up data into categories. To get access to a preference file, you need to request a Preferences instance by its filename as follows:

Preferences prefs = Gdx.app.getPreferences("settings.prefs");

To write a (new) value, you have to choose a key under which the value should be stored. If this key already exists in a preferences file, it will be overwritten. Do not forget to call flush() afterwards to persist the data, or else all the changes will be lost.

prefs.putInteger("sound_volume", 100); // volume @ 100%
prefs.flush();

To read back a certain value from a preferences file, you need to know the corresponding key. If this key does not exist, it will be set to the default value. You can optionally pass your own default value as the second argument (for example, in the following listing, 50 is for the default sound volume):

int soundVolume = prefs.getInteger("sound_volume", 50);

On Android, you can query the Android API Level, which allows you to handle things differently for certain versions of the Android OS. Use the following listing to find out the version:

Gdx.app.getVersion();

You may want to write a platform-specific code where it is necessary to know the current platform type. The following example shows how it can be done:

switch (Gdx.app.getType()) {
  case Desktop:
  // Code for Desktop application
  break;
  case Android:
  // Code for Android application
  break;
  case WebGL:
  // Code for WebGL application
  break;
  default:
  // Unhandled (new?) platform application
  break;
}

You can query the system to find out its current memory footprint of your application. This may help you find excessive memory allocations that could lead to application crashes. The following functions return the amount of memory (in bytes) that is in use by the corresponding heap:

long memUsageJavaHeap = Gdx.app.getJavaHeap();
long memUsageNativeHeap = Gdx.app.getNativeHeap();

Query Libgdx for the time span between the current and the last frame in seconds by calling Gdx.graphics.getDeltaTime().

Query the device's display size returned in pixels by calling Gdx.graphics.getWidth() and Gdx.graphics.getHeight().

Query a built-in frame counter provided by Libgdx to find the average number of frames per second by calling Gdx.graphics.getFramesPerSecond().

To load sounds for playback, call Gdx.audio.newSound().

The supported file formats are WAV, MP3, and OGG.

There is an upper limit of 1 MB for decoded audio data. Consider the sounds to be short effects like bullets or explosions so that the size limitation is not really an issue.

To stream music for playback, call Gdx.audio.newMusic().

The supported file formats are WAV, MP3, and OGG.

Query the system for the last x or y coordinate in the screen coordinates where the screen origin is at the top-left corner by calling either Gdx.input.getX() or Gdx.input.getY().

Query the accelerometer for its value on the x axis by calling Gdx.input.getAccelerometerX(). Replace the X in the method's name with Y or Z to query the other two axes. Be aware that there will be no accelerometer present on a desktop, so Libgdx always returns 0.

On Android, you can let the device vibrate by calling Gdx.input.vibrate().

A running vibration can be cancelled by calling Gdx.input.cancelVibrate().

You might want to catch Android's soft keys to add an extra handling code for them. If you want to catch the back button, call Gdx.input.setCatchBackKey(true). If you want to catch the menu button, call Gdx.input.setCatchMenuKey(true).

On a desktop where you have a mouse pointer, you can tell Libgdx to catch it so that you get a permanent mouse input without having the mouse ever leave the application window. To catch the mouse cursor, call Gdx.input.setCursorCatched(true).

You can get a file handle for an internal file by calling Gdx.files.internal().

An internal file is relative to the assets folder on the Android and WebGL platforms. On a desktop, it is relative to the root folder of the application.

You can get a file handle for an external file by calling Gdx.files.external().

An external file is relative to the SD card on the Android platform. On a desktop, it is relative to the user's home folder. Note that this is not available for WebGL applications.

You can make HTTP GET and POST requests by calling either Gdx.net.httpGet() or Gdx.net.httpPost().

You can create client/server sockets by calling either Gdx.net.newClientSocket() or Gdx.net.newServerSocket().

To open a Uniform Resource Identifier (URI) in the default web browser, call Gdx.net.openURI(URI).