What are dex files in Android

Question

I have some questions regarding dex files    What is a dex file in Android  How does dex work for Android  How are they used in debugging an Android app  Are they similar to java class files    I need specific information please help on this and any real examples are  welcome

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dex file   Compiled Android application code file   Android programs are compiled into  dex  Dalvik Executable  files  which are in turn zipped into a single  apk file on the device   dex files can be created automatically by Android  by translating the compiled applications written in the Java programming language

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dex file is a file that is executed on the Dalvik VM   Dalvik VM includes several features for performance optimization  verification  and monitoring  one of which is Dalvik Executable  DEX    Java source code is compiled by the Java compiler into  class files  Then the dx  dexer  tool  part of the Android SDK processes the  class files into a file format called DEX that contains Dalvik byte code  The dx tool eliminates all the redundant information that is present in the classes  In DEX all the classes of the application are packed into one file  The following table provides comparison between code sizes for JVM jar files and the files processed by the dex tool    The table compares code sizes for system libraries  web browser applications  and a general purpose application  alarm clock app   In all cases dex tool reduced size of the code by more than 50      In standard Java environments each class in Java code results in one  class file  That means  if the Java source code file has one public class and two anonymous classes  let   s say for event handling  then the java compiler will create total three  class files   The compilation step is same on the Android platform  thus resulting in multiple  class files  But after  class files are generated  the    dx    tool is used to convert all  class files into a single  dex  or Dalvik Executable  file  It is the  dex file that is executed on the Dalvik VM  The  dex file has been optimized for memory usage and the design is primarily driven by sharing of data

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About the  dex File    One of the most remarkable features of the Dalvik Virtual Machine  the workhorse under the Android system  is that it does not use Java bytecode  Instead  a homegrown format called DEX was introduced and not even the bytecode instructions are the same as Java bytecode instructions    Compiled Android application code file    Android programs are compiled into  dex  Dalvik Executable  files  which are in turn zipped into a single  apk file on the device   dex files can be created by automatically translating compiled applications written in the Java programming language   Dex file format    1  File Header  2  String Table  3  Class List  4  Field Table  5  Method Table  6  Class Definition Table  7  Field List  8  Method List  9  Code Header 10  Local Variable List   Android has documentation on the Dalvik Executable Format   dex files   You can find out more over at the official docs  Dex File Format   dex files are similar to java class files  but they were run under the Dalkvik Virtual Machine  DVM  on older Android versions  and compiled at install time on the device to native code with ART on newer Android versions   You can decompile  dex using the dexdump tool which is provided in android-sdk   There are also some Reverse Engineering Techniques to make a jar file or java class file from a  dex file

[android] What are .dex files in Android?

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