什么是Dalvik【摘】

To understand Dalvik, you must first understand that Android is not Java. Android is “Java based”. Android programs take an additional step after Java file is compiled into Java bytecode. The Java bytecode will then be converted into Dalvik bytecode. This is because Android does not have a Java virtual machine. Dalvik replaces the Java VM on the Android platform. Dalvik differs from the Java virtual machine in a number of ways. Many of these differences are necessary because mobile phones typically have lower memory and less powerful hardware than the platforms that Java typically runs on.

When you run more than one Java program at a time, each program starts its own virtual machine. Parts of the VM are read-only but each Java VM has its own copy of those read-only portions. To optimize the low memory environment of most mobile devices, Dalvik has been designed to share a single copy of the read-only parts of the virtual machine. When your Android phone runs more than one application at a time, each application runs in its own Dalvik virtual machine. However, all of those Dalvik virtual machines share a single copy of the read-only portions. This greatly reduces memory consumption.

The Dalvik machine is register-based rather than stack-based like the Java virtual machine. In a stack based machine, the computer’s memory forms a stack. Instructions are taken from the top of the stack and moved into memory for execution. Register based systems use a series of memory registers rather than a stack. By being a register based machine, Dalvik can get better performance from a limited memory architecture.

 

原文=>http://www.learncomputer.com/what-is-dalvik/