On Day 1, I learned about JDK and how a .java file becomes a .class file.
Today, we moved to the second level of translation in Java and also started learning about Data Types.
🔁 Second Level of Translation (Platform Dependent)
After JDK creates the .class file (Bytecode), what happens next?
This is where:
JRE
JVM
JIT
come into action.
🧩 JRE – Java Runtime Environment
JRE provides the environment required to run Java programs.
It contains:
Required libraries
Supporting files
Predefined .class files
Without JRE, Java programs cannot run.
⚙️ JVM – Java Virtual Machine
JVM is responsible for:
Running the .class file
Managing memory
Converting bytecode into machine-understandable instructions
It acts like a bridge between Java and the operating system.
⚡ JIT – Just In Time Compiler
JIT improves performance.
It converts bytecode into native machine code (0s and 1s) at runtime, making execution faster.
💻 Compiling and Running a Java Program
Today we also practiced running Java programs manually using Command Prompt.
To Compile:
javac FileName.java
To Run:
java FileName
Important:
Do NOT include .class while running.
Just type the file name.
📦 What is a Data Type?
Data Type is like a container.
It defines:
What type of data we store
How much memory it uses
Different data types store different types of values.
🔢 Numeric Data Types
Integer Types:
byte
short
int
long
Example:
int age = 25;
long distance = 100000L;
Decimal Types:
float
double
Example:
float price = 10.5f;
double salary = 10000.75;
🔤 Character Type
char
Example:
char grade = 'A';
✅ Boolean Type
boolean
Example:
boolean isJavaFun = true;
Only two values:
true
false
🧠 Simple Understanding of Data Types
Our trainer explained it in a very simple way:
Imagine different water bottles:
1 liter bottle
5 liter bottle
10 liter bottle
You cannot store 10 liters in a 1 liter bottle.
Similarly:
Small values → small data types
Large values → large data types
Choosing the correct data type is important.
🎯 My Learning Reflection – Day 2
Today I understood:
✔ Java has two levels of translation
✔ How JRE, JVM, and JIT work
✔ How to compile and run Java manually
✔ What data types are and why they matter
Step by step, I am building my foundation.
My goal remains the same:
To become a Master in Automation Testing using Selenium and Playwright.
Strong basics in Java = Strong automation skills.
👨🏫 Trainer: Nantha from Payilagam
🤖 A Small Note
I used ChatGPT to help structure and refine this blog while ensuring the concepts remain aligned with my trainer’s explanations.
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