Review Java 9 Concepts at Jet Speed.

• Platform Independent or Portable
• Object Oriented Language
• Security
• Rich API
• Great IDE's
• Omnipresent
  • Web Applications (JSP, Servlets, Spring, Struts..)
  • Mobile Apps(Android)
  • Microservices (Spring Boot)

• Build once, run anywhere
• Java bytecode is the instruction set of the Java virtual machine

graph TD
A[Java Code] -->|Compiled| B(Bytecode)
B --> C{Run}
C -->|bytecode| D[Windows JVM] 
D --> K[Windows Instructions]
C -->|bytecode| E[Unix  JVM]
E --> L[Unix Instructions]
C -->|bytecode| F[Linux  JVM]
F --> M[Linux Instructions]
C -->|bytecode| G[Any other platform  JVM]
G --> N[Linux Instructions]

• JVM (Java Virtual Machine)
  • runs the Java bytecode.
• JRE
  • JVM + Libraries + Other Components (to run applets and other java applications)
• JDK • JRE + Compilers + Debuggers

• Find and Loads Java Classes!

Three Types

• System Class Loader - Loads all application classes from CLASSPATH
• Extension Class Loader - Loads all classes from extension directory
• Bootstrap Class Loader - Loads all the Java core files

JVM needs to find a class, it starts with System Class Loader. If it is not found, it checks with Extension Class Loader. If it not found, it goes to the Bootstrap Class Loader. If a class is still not found, a ClassNotFoundException is thrown.