Java virtual machine

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

The JVM (Java Virtual Machine) 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)

• 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

 

JVM (Java Virtual Machine) Architecture

The architecture of the HotSpot JVM 3 is shown below −