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Applications designed for BlackBerry® devices should provide a balance between the best possible user experience and a long battery life. When you design your BlackBerry device application, consider the differences between mobile devices and computers. Mobile devices have the following characteristics:

• A smaller screen size that can display a limited number of characters
• Slower processor speeds
• Wireless network connections with a longer latency period than standard LANs
• Less available memory
• Shorter battery life
• One screen appears at a time

Mobile device users use applications on their mobile devices differently than they would use applications on a computer. On mobile devices, users expect to find information quickly. For example, a customer relationship management system can provide a massive amount of information, but users only require a small amount of that information at one time. The BlackBerry device UI is designed so that users can perform tasks easily and access information quickly.

Before you design your application, consider using the existing applications on the BlackBerry device or the BlackBerry Smartphone Simulator to learn more about the navigation model and best practices for designing the UI for your application.

Android Architecture

What is Android?

First of all Android is not a mobile phone brand. It’s a software stack for mobile devices that includes an operating system, middleware and key applications. The Android SDK provides the tools and APIs necessary to begin developing applications on the Android platform using the Java programming language.

It’s very easy to handle events on Android SDK. It’s just like you are doing a Java Swing application.

Features

• Application framework enabling reuse and replacement of components
• Dalvik virtual machine optimized for mobile devices
• Integrated browser based on the open source WebKit engine
• Optimized graphics powered by a custom 2D graphics library; 3D graphics based on the OpenGL ES 1.0 specification (hardware acceleration optional)
• SQLite for structured data storage
• Media support for common audio, video, and still image formats (MPEG4, H.264, MP3, AAC, AMR, JPG, PNG, GIF)
• GSM Telephony (hardware dependent)
• Bluetooth, EDGE, 3G, and WiFi (hardware dependent)
• Camera, GPS, compass, and accelerometer (hardware dependent)
• Rich development environment including a device emulator, tools for debugging, memory and performance profiling, and a plugin for the Eclipse IDE

Applications

Android will ship with a set of core applications including an email client, SMS program, calendar, maps, browser, contacts, and others. All applications are written using the Java programming language.

Application Framework

The open development platform provides the ability for developers to build extremely rich and innovative applications. Developers are free to take advantage of the device hardware, access location information, run background services, and add notifications to the status bar and much more.

Developers have full access to the same framework APIs used by the core applications. The application architecture is designed to simplify the reuse of components; any application can publish its capabilities and any other application may then make use of those capabilities (subject to security constraints enforced by the framework).

Libraries

Android includes a set of C/C++ libraries used by various components of the Android system. These capabilities are exposed to developers through the Android application framework.

Android Runtime

Android includes a set of core libraries that provides most of the functionality available in the core libraries of the Java programming language.

Every Android application runs in its own process, with its own instance of the Dalvik virtual machine. Dalvik has been written so that a device can run multiple VMs efficiently. Dalvik is optimized for minimal memory footprint. The VM is register-based, and runs classes compiled by a Java language compiler that have been transformed into the .dex format by the included “dx” tool.

The Dalvik VM relies on the Linux kernel for underlying functionality such as threading and low-level memory management.

Linux Kernel

Android relies on Linux version 2.6 for core system services such as security, memory management, process management, network stack, and driver model. The kernel also acts as an abstraction layer between the hardware and the rest of the software stack.

Java ME technology was originally created in order to deal with the constraints associated with building applications for small devices. For this purpose Sun defined the basics for Java ME technology to fit such a limited environment and make it possible to create Java applications running on small devices with limited memory, display and power capacity.

Java ME platform is a collection of technologies and specifications that can be combined to construct a complete Java run time environment specifically to fit the requirements of a particular device or market. This offers a flexibility and co-existence for all the players in the eco-system to seamlessly cooperate to offer the most appealing experience for the end-user.

The Java ME technology is based on three elements;

• A configuration provides the most basic set of libraries and virtual machine capabilities for a broad range of devices,
• A profile is a set of APIs that support a narrower range of devices, and
• An optional package is a set of technology-specific APIs.

Over time the Java ME platform has been divided into two base configurations, one to fit small mobile devices and one to be targeted towards more capable mobile devices like smart-phones and set top boxes.

The configuration for small devices is called the Connected Limited Device Configuration (CLDC) and the more capable configuration is called the Connected Device Configuration (CDC).

The figure below represents an overview of the components of Java ME technology and how it relates to the other Java Technologies.