Differences between JVM, Dalvik and art

JVM、Dalvik and ART The difference between

Generally speaking, traditional Java Virtual machine is JVM, later Google And I am dedicated to Android Platform design Java virtual machine , That's it Dalvik and ART, and ART It's right again Dalvik A full upgrade of .

Now the problem focuses on Dalvik And ART It's on you , Both of them are Android Virtual machine on platform ,Android The application uses a suffix named .apk The compressed file of , Let's first analyze Apk file .Apk The file mainly includes some resource files , Inventory file , and classes.dex file （classes If the method is divided by more than 65536 Will result in packaging failure , You can use MutiDex to subcontract , The main principle is to increase classes file ）,classes.dex File by java Bytecode Optimized and packaged , There are two situations ：

• Dalvik virtual machine ： stay Dalvik in , Every time you open an application ,Dalvik Will read classes.dex Document and explain the implementation ,Dalvik Rely on one Just-In-Time(JIT) Compiler to interpret bytecode . This interpretation is not efficient , But it makes it easier for applications to be compatible with different hardware and architectures .Dalvik optimized , Allow multiple instances of virtual machines to run in limited memory , And each of these Dalvik Apply as an independent Linux Process execution . Independent processes can prevent all programs from being shut down when the virtual machine crashes .

• ART virtual machine ： Use Ahead-Of-Time（AOT） Compiling mechanism , When the application is installed, the bytecode is precompiled into the machine language and saved locally , The suffix is oat The file of , Then open the application and directly read the local machine language , Efficiency has been greatly improved .

ART contrast Dalvik Advantages and disadvantages （ Comparison between similar interpretive languages and compiled languages ）：

• advantage ：

  1. The system performance is significantly improved .
  2. Apps start faster 、 Run faster , More fluid experience , Touch feedback is more timely .
  3. Longer battery life .

• shortcoming ：

  1. Larger storage footprint , May increase 10%~20%.
  2. Longer application installation time .

in general ART The effect is Space for time

Reference resources ：
http://www.cnblogs.com/shaweng/p/3811461.html
https://www.zhihu.com/question/29406156