purpose
Virtual machine has always felt very mysterious. I have forgotten a little bit after learning a few years ago. I have read the book "In-depth Understanding of JAVA Virtual Machine" several times this year, and gradually I have a bit of common sense understanding, but it is still not deep enough. So I want to organize the process I want to learn into notes for easy reference later.
Defining the
JAVA virtual machine is the cornerstone of the entire JAVA platform. It is a key part of JAVA technology to realize hardware-independent and operating system-independent. It is a running platform where JAVA language generates a very small volume of compiled code and protects user machines from malicious code. Barrier to damage.
JAVA virtual machine can be regarded as an abstract computer, like a real computer, it has its own instructions and various runtime memory areas.
The JAVA virtual machine is not necessarily related to the JAVA language. It is only associated with a specific binary file format (class). The class file contains the JAVA virtual machine instruction set and symbol table, as well as some other auxiliary information.
One-time compilation,
the default compilation result of running JAVA source code everywhere is not executable machine code, but a platform-general bytecode. Although the implementation mechanisms of JAVA virtual machines on different platforms are not the same, they explain the words together The section code is the same, so bytecode is the key element for JAVA to achieve cross-platform.