Java Virtual Machine - Introduction

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The JVM is a specification, and can have different implementations, as long as they adhere to the specs. The specs can be found in the below link − https://docs.oracle.com

Oracle has its own JVM implementation (called the HotSpot JVM), the IBM has its own (the J9 JVM, for example).

The operations defined inside the spec are given below (source − Oracle JVM Specs, see the above link) −

  • The ‘class’ file format
  • Data types
  • Primitive types and values
  • Reference types and values
  • Run-time data areas
  • Frames
  • Representation of objects
  • Floating-point arithmetic
  • Special methods
  • Exceptions
  • Instruction set summary
  • Class libraries
  • Public design, private implementation

The JVM is a virtual machine, an abstract computer that has its own ISA, own memory, stack, heap, etc. It runs on the host OS and places its demands for resources to it.

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