Dalvik, Android virtual machine
Dalvik was a virtual machine for the Java language of Google's Android operating system applications. She was replaced by ART.
The name comes from the city of Iceland, where the creator comes from. Dalvik produces the Open Handset Alliance, which brings together about 100 companies .
It was created to replace the Java virtual machine, since even if it is licensed GPL2 in the regular version, there is an exception on the mobile version of Java ME, which allows Oracle to request rights to use it.
Android applications are written in Java, the code is first compiled into bytecode by a classic Java compiler, and then recompiled into code recognizable by Dalvik .
The .class files are converted to a .dex file. But such a file includes several classes and is equivalent in size to a jar file.
Dulwick does not use a Java classes bookstore, but a pure bookstore based on the Apache foundation's alternative, Harmony. Android does not use either the Java ME virtual machine or the Java SE library.
Dalvik is a JIT (Just In Time) machine, it compiles bytecode in real time, but in the future will be replaced by the AOT compiler, which compiles and stores the bytecode before execution. This new virtual machine, called ART (Android RunTime), is still in development in 2014 and works on an option in Android 4.4. Bytecode in the .dex file also remains developer-compatible.
Dalvik vs. Java ME
There are differences between virtual machines, in particular, Dalvik runs applications in a clean environment, as browsers do, which is safer .
Two quotes in the Android documentation summarize the difference between Dalvik and Java Micro Edition :
"Each Android application rotates in its own process, which is its personal instance of the Dalvik virtual machine. "Dalvik" was written so that one material could run efficiently on multiple MVs. "
"MV Dalvik runs files in Dalvik Executable (.dex) format, optimized for minimum memory usage. MV is case-based and rotates classes compiled by the Java language compiler that have been converted to .dex format by the tool includes "dx.""
In addition, some of the functions were postponed to the back end, in this case Linux:
"MV Dalvik depends on kernel Linux for system functions such as processes and low-level memory management."
Source: Android developer site Translation of quotes by .fr.
Other virtual machines
Dalvik Turbo: Created by Myriad, a compatible virtual machine that wants Dalvik faster.
ART: Google's new virtual machine running in AOT.
Oracle vs. Dalwick
On August 12, 2010, Oracle, which bought Sun and thus Java in 2009, filed a complaint against Google for copyright and patent infringement.
The main subject of this complaint is the Dalvik virtual machine, which, according to the complaint, used technologies covered by software patents that Oracle now allegedly owns.
Google responded, believing that the complaint had no basis, and that Dalvik was a product of the Open Handset Alliance, not Google.
The outcome of the trial concerned the validity of the software patents allegedly used at Dalvik.
It should be understood that with the huge popularity of Android (which as of August 2010 was sold in a circulation of 200 thousand copies per day), the Oracle JME virtual machine cannot bring them anything. Android has even been ported to devices designed for other operating systems such as RIM.
But would Java ME be chosen by manufacturers as the engine of their applications while it is subject to royalties?
Update 2013: Oracle lost a lawsuit against Google in the first instance. He appealed but dropped the patent claims, otherwise he invoked the Java API, which he says is copyrighted, it's novelty. On call, the Oracle took over.
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