🚀 Day 2 of My Automation Journey – Understanding JRE, JVM, JIT & Data Types

Source: Dev.to

Introduction

On Day 1, I learned about the JDK and how a .java file becomes a .class file.
Today I moved to the second level of translation in Java and started learning about data types.

Second Level of Translation (Platform Dependent)

JRE – Java Runtime Environment

• Contains the required libraries.
• Without the JRE, Java programs cannot run.

JVM – Java Virtual Machine

• Executes the .class file.

JIT – Just‑In‑Time Compiler

• Improves performance by compiling bytecode to native code at runtime.

Compiling and Running a Java Program

To compile:

javac FileName.java

To run:

java FileName

Important: Do not include the .class extension when running; just type the file name.

What is a Data Type?

A data type defines:

• What kind of data we store.
• How much memory it uses.

Different data types store different kinds of values.

Numeric Data Types

Integer Types

int age = 25;
long distance = 100000L;

Decimal Types

float price = 10.5f;
double salary = 10000.75;

Character Type

char grade = 'A';

Boolean Type

boolean isJavaFun = true;

Only two possible values: true or false.

Simple Understanding of Data Types

Imagine different water bottles: a 1‑liter bottle cannot hold 10 liters.
Similarly, small values should be stored in small data types.

My Learning Reflection – Day 2

• Java has two levels of translation.
• Step by step, I am building my foundation.

My goal remains the same: Strong basics in Java = Strong automation skills.

Date: 19/02/2026

Note: I used ChatGPT to help me structure and refine this blog.