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Android Dalvik Virtual Machine

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In this article we are discussing about the Dalvik Virtual Machine. It is one of the important concept in android architecture. Dalvik Virtual Machine has also been asked few times in university exams (sometimes as a separate question and sometimes along with the Android Architecture).

Dalvik Virtual Machine is one of the key elements of Android Application. The Dalvik Virtual Machine (DVM) is an android virtual machine which is optimized for mobile devices. It optimizes the virtual machine for memory, battery life and performance. Dalvik Virtual Machine is only supported by the android operating system. The overall execution is faster using Dalvik VM.

Rather than using a traditional Java Virtual Machine, Android uses its own custom VM, designed to ensure that multiple instances run efficiently on a single device. One reason for using Dalvik VM is that Java VM was not open source and hence not efficient to use on a large scale.

The Dalvik Virtual Machine uses the device’s underlying Linux kernel to handle some low-level functionality, including security, threading, process management and memory management.

Dalvik acts as a middle person between hardware and system service access. By using a VM to host application execution, developers have an abstraction layer that ensures that they never have to worry about a particular hardware implementation.

The Dalvik VM executes Dalvik executable files (DEX). The Dex files are optimized for minimal memory usage. The Dex compiler converts the ".class" files into the ".dex" files that runs on the Dalvik Virtual Machine. Multiple class files are converted into single dex file. 


Working of Dex Compiler

Basically, the Java Compiler (javac) converts the Java Source Code into Java Byte-Code. This is the ".class file". Now this ".class" file is compiled by DEX compiler to obtain a ".dex" file (Dalvik Byte Code) which is then packaged by the AAPT (Android Assets Packaging Tool) into a ".apk" file.

 


Also checkout Android Architecture and the Different Building Blocks of Android.

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