JVM (1) JVM Internals : What does JVM do?

 

 Some basic concepts:

What is the difference between JVM, JRE, and JDK

JVM:  Java Virtual Machine 

　　　It Provides Runtime Environment in which Java bytecode can by executed,

　　　Tasks of JVM :  Loads Code 

　　　　　　　　　　Verifies Code 

　　　　　　　　　　Executes Code 

　　　　　　　　　　Provides Runtime Environment

　　　　　　　　　　JVM is platform dependent, i.e for each software and hardware we have different JVM configuaration

　　　　　　　　　　JVM does not exists physically, it is abstract in nature.

 

JRE: It stands for Java Runtime Environment. 

　

 

　　　JRE->  JVM + Set of libraries 

　　　　　　It is the implementation of JVM

　　　　　　To run any java code JRE is minimum required. 

　　　　　　JRE contains set of libraies that JVM uses at runtime

　　　　　　JRE physically exists.

　　　　　　JRE is platform dependent.

 

JDK: 

 

JDK stands for Java Development Kit

JDK -> JRE+Development Tools

it is a full featured Software Development Kit 

It contains JRE+Development Tools (Debugger + Compiler + JavaDoc etc)

To Conclude :

　　

 

JVM Internals : What does JVM do?

 

when we write and execute a java code, below are some of the common way we do that. 

 

 

And below is how JVM instance load and excecute our class files. 

Class Load is responsible for loading our .class file , which in above example is MyApp.class, it is also responsible for loading some of the built-in .class files 

 

 

 

 Class Loading SubSystem has three main faces:

Load: 1. Bootstrap class Loader

　　　2. Extension Class Loader

　　　3. Application Class Loader

Link:  　　1. Verify:  

　　　　　2. Prepare:

　　　　　3. Resolve:

Initialize