Java Basics: Language, Compiler, JVM, JRE, and JDK

Study Notes

Java Language

Java syntax is derived from C and OOPS features are derived from C++.
Java has its own syntax, rules, format, and programming paradigm.

Java Compiler

Function is to generate Java class files from the Java source code.
Class file contains a platform-independent Java byte code.

Java Virtual Machine (JVM)

JVM is platform-independent, converting byte code into machine-specific code.
Provides functionality of garbage collection, memory management, security, etc.
Allows creating Java programs on one machine and executing them on another machine (WORA – Write – Once – Run – Anywhere).
JVM is present on the RAM.
Loads generated class files and either interprets the byte code or compiles it to machine code using Just-in-time (JIT) compiler.

Class Loader

Used to load class files.
Responsible for loading, linking, and initialization of the program to be executed.
Brings the class file to the RAM for execution.
Verifies the BYTE code for any security issues.

JVM Memory

Contains components that help in the execution of the program.
Holds PC registers that contain the current instruction to be executed.
Heap holds variables, arrays, etc.
Method area holds method code.
Native method stack holds native language specification.
JVM stack holds the instance of the program or the current thread.
Each thread has its own JVM stack.

Execution Engine

Cooperates with the native method interface and native method libraries.
Converts Bytecode into native machine code using just-in-time (JIT) compiler.
JIT interprets a part of the Byte Code that has similar functionality at the same time.

Method Area

One of the data areas in JVM, storing Class data.
Static Variables, Static Blocks, Static Methods, and Instance Methods are stored in this area.

Heap

Created when the JVM starts up.
May increase or decrease in size while the application runs.
Used for dynamic memory allocation of Java objects and JRE classes at runtime.

Stack

JVM stack is known as a thread stack.
Used to store local variables, partial results, and data for calling method and returns.

Native Stack

Subsumes all the native methods used in the application.

Description

Test your knowledge of the Java programming language, its compiler, Java Virtual Machine (JVM), Java Runtime Environment (JRE), and Java Development Kit (JDK). Learn about Java syntax, OOPS features, and platform-independent byte code.