The Dalvik Virtual Machine davidehringer（davidehringer Dalvik虚拟机）.pdf

David Ehringer March, 2010 T H E D A LV I K V I RT U A L M A C H I N E A R C H I T E C T U R E Introduction Java has always been marketed as “write once, run anywhere.” The capability has largely been made possible by the Java Platform, the foundation of which is the Java Virtual Machine (JVM). Although this goal has largely been met for the Java platform on desktop (JSE) and server (JEE) environments, the mobile Java ecosystem (JME) is a bit more fragmented with various configurations, profiles, and packages causing significant modifications to applications in order to support different devices. While Google has selected Java as the language for developing Android applications, it has chosen to abandon both JME and the JVM in favor of an alternative deployment target, the Dalvik virtual machine. Google has also chosen to use an alternative and limited implementation of the standard Java libraries. Both of these are non-standard Java, and effectively represent forking of the Java platform. This seems to break from the trend of people targeting the JVM as a the runtime platform for a very wide range of languages. Scala, Groovy, JRuby, Jython, and Clojure are only a few of the dozens of languages that run on the JVM. These languages can not only take advantage of the many features of the JVM but also seamlessly leverage all the standard Java libraries and the countless custom libraries created by individuals and organizations. Recently, Google has been subtlety bucking this trend by created non-standard Java technologies. This includes non only the Android platform but also Google Web Toolkit (GWT) and Google App Engine, the reasons of which they are non-standard is beyond the scope of this paper as they aren’t mobile technologies. But the trend may be applicable to what has happened in the JME space. Non-standard Java implementations may further fragment the platform cause additional headaches for developers look