WEBVTT 00:01.440 --> 00:07.530 So far in this course, steps have been taken to set up an environment suitable for the development 00:07.530 --> 00:10.160 of Android applications using Android studio. 00:10.170 --> 00:16.380 An initial step has also been taken into the process of application development through the creation 00:16.410 --> 00:19.020 of Android Studio Application Project. 00:19.050 --> 00:25.650 Before delving further into practical matters of Android application development, however, it is important 00:25.650 --> 00:31.230 to gain an understanding of some of the more abstract concepts of both Android software development 00:31.230 --> 00:33.960 kit and Android development in general. 00:34.140 --> 00:41.850 Gaining a clear understanding of these concepts now will provide a sound foundation on which to build 00:41.850 --> 00:43.050 further knowledge. 00:43.050 --> 00:49.230 So starting with an overview of Android of Android application in this course and continuing to in the 00:49.230 --> 00:56.640 next few lectures of this course, the goal is to provide a detailed overview of the fundamentals of 00:56.640 --> 00:58.140 Android development. 00:58.170 --> 01:01.260 My name is Stephan and let's get started with our lecture. 01:13.410 --> 01:21.930 The Android software stack on Android is a structured in the form of software stack comprising applications 01:21.930 --> 01:26.700 and operating systems, runtime, environment, middleware services and libraries. 01:26.970 --> 01:34.920 This architecture can perhaps can best be represented visually as outlined in this screenshot. 01:35.100 --> 01:42.060 Each layer of the stack and the corresponding elements within each layer are tightly integrated and 01:42.060 --> 01:48.720 carefully tuned to provide the optimal application, development and execution environment for mobile 01:48.720 --> 01:49.500 devices. 01:49.530 --> 01:56.610 The remainder of this course will work through the different layers of this Android stack and starting 01:56.670 --> 01:59.490 the bottom with the Linux kernel. 02:00.190 --> 02:02.920 So let's get started with the Linux kernel. 02:03.600 --> 02:08.310 Linux kernel positioned at the bottom of Android software stack. 02:08.340 --> 02:15.300 The Linux kernel provides a level of abstraction between the device hardware and upper layers of Android 02:15.300 --> 02:19.540 software stack based on Linux version 2.6. 02:19.560 --> 02:26.940 The kernel provides a preemptive multitasking, low level core system services such as memory process 02:26.940 --> 02:28.470 and power management. 02:28.470 --> 02:35.580 In addition to providing a network stack and device drivers for hardware such as device displays, WiFi 02:35.580 --> 02:36.900 and audio. 02:37.230 --> 02:47.430 The original Linux kernel was developed by in 1991 by Linus Torvalds and was combined with a set of 02:47.430 --> 02:55.200 tools, utilities and compilers developed by Richard Stallman at the Free Software Foundation to create 02:55.200 --> 02:59.430 a full operating system referred to as Genie or Linux. 02:59.460 --> 03:07.660 The various Linux distributions have been derived from the basic underpinnings such as Ubuntu and Red 03:07.690 --> 03:09.400 Hat Enterprise Linux. 03:09.430 --> 03:15.990 The Kali Linux and the Ubuntu and other Linux based systems. 03:16.000 --> 03:22.630 And it's important to note, however, that Android uses only the Linux kernel. 03:22.660 --> 03:31.030 That said, it is worth noting that the Linux kernel was originally developed for use in traditional 03:31.030 --> 03:33.610 computers in the form of desktops and servers. 03:33.640 --> 03:41.260 In fact, Linux is now most widely deployed in mission critical enterprise server environments and it 03:41.260 --> 03:48.160 is a testament to both the power of today's mobile devices and the efficiency and performance of the 03:48.160 --> 03:54.370 Linux kernel that we find this software at the heart of the Android software stack. 03:55.680 --> 04:03.930 In addition to a set of standard Java Kotlin Development libraries, this providing a support for such 04:03.930 --> 04:10.590 general purpose tasks such as string handling, networking and file manipulation. 04:10.620 --> 04:15.930 The Android development environment also includes the Android libraries. 04:16.260 --> 04:21.810 These are a set of Java based libraries that are specific to Android development. 04:21.840 --> 04:27.840 Examples of libraries in this category include the application framework libraries in addition to those 04:27.840 --> 04:34.740 that facilitate user interface building, graphics, drawing and database access. 04:34.740 --> 04:40.080 And on the screen you are seeing some of the most used libraries in Android. 04:44.020 --> 04:45.700 The Android runtime. 04:45.700 --> 04:52.960 Core libraries, as outlined in the preceding section, are Java and Kotlin based and provide the primary 04:52.990 --> 04:56.050 APIs for developers writing Android application. 04:56.170 --> 05:03.340 And it's important to note that, however, that the core libraries do not perform much of the actual 05:03.340 --> 05:11.770 work and are in fact essentially Java and Kotlin wrappers around a set of C and C plus plus based libraries. 05:11.770 --> 05:20.620 So when making a calls, for example, the Android OpenGL library to drive 3D graphics on the device 05:20.620 --> 05:28.870 display and the library actually ultimately makes a call to the OpenGL s C plus plus library, which 05:28.900 --> 05:35.230 in turn works with the underlying Linux kernel to perform the driving tasks. 05:35.470 --> 05:42.760 The C plus plus libraries are included to fulfill a wide and diverse range of functions, including 05:42.790 --> 05:52.250 2D and 3D graphics drawing secure sockets, layer, SSL communication, SQLite database management, 05:52.280 --> 06:00.710 audio and video playback bitmap and vector font rendering display subsystem and graphics layer management 06:00.710 --> 06:04.610 and an implementation of the standard C System library. 06:05.060 --> 06:06.860 This means the lib C here. 06:06.860 --> 06:13.730 So in practice, the typical Android application developer will access these libraries solely through 06:13.730 --> 06:17.790 Java or Kotlin based Android core library APIs. 06:17.810 --> 06:24.860 In the event that direct access to these libraries is needed, this can be achieved using the Android 06:24.890 --> 06:28.370 Native Development kit in the UK. 06:28.520 --> 06:34.940 So the purpose of which is to call the native methods of Non-java or Kotlin programming languages such 06:34.940 --> 06:42.650 as C and C plus plus from within the Java and Kotlin code using the Java Native interface G and I. 06:43.640 --> 06:49.310 And lastly, we have left to discuss the application framework in Android architecture. 06:49.430 --> 06:56.360 The application framework is a set of services that collectively form the environment in which applications 06:56.360 --> 06:59.720 and other applications run and are merged. 06:59.750 --> 07:06.650 This framework implements the concepts that Android applications are constructed from a reusable, interchangeable 07:06.650 --> 07:13.130 and replaceable components, and this concept is taken a step further in that an application is also 07:13.130 --> 07:20.960 able to publish its capabilities along with any corresponding data so that they can be found and reused 07:20.960 --> 07:23.060 by other applications. 07:23.060 --> 07:24.410 So they are following. 07:24.410 --> 07:30.890 The Android framework includes, for example, activity manager, which you can see on the screen here. 07:30.890 --> 07:39.530 So the applications here located at the top of the Android software stack are the applications. 07:39.530 --> 07:45.450 So these comprise both the native applications provided with the particular Android implementations, 07:45.450 --> 07:51.840 for example, web browser and the email applications and the third party applications installed by the 07:51.840 --> 07:54.990 user after processing the device. 07:56.970 --> 08:03.090 A good Android Development Knowledge Foundation requires an understanding of the overall architecture 08:03.090 --> 08:03.960 of Android. 08:04.050 --> 08:09.930 Android is implemented in the form of software stack architecture, consisting of a Linux kernel, a 08:09.930 --> 08:15.720 runtime environment and corresponding libraries, an application framework and a set of applications. 08:15.720 --> 08:23.130 So applications are predominantly written in Java or Kotlin and compiled down to bytecode format within 08:23.130 --> 08:25.380 the Android studio build environment. 08:25.410 --> 08:32.670 When an application is subsequently installed on a device, this byte code is compiled down by the Android 08:32.670 --> 08:38.310 runtime art to the native format used by the CPU. 08:38.460 --> 08:46.320 The key goals of the Android architecture are performance and efficiency, so both in application execution 08:46.320 --> 08:50.550 and the implementation of reuse in application design.