This content originally appeared on DEV Community and was authored by Rohit Juyal
Java Learning Journey: Day 02 ✨
Date: 25 Sept, 2025
Hello everyone 👋 Today I wrote my very first Java program:
public class Hello {
public static void main(String[] args) {
System.out.print("Hello java");
}
}
🔎 Breaking Down the Code
Semicolon ;
- Tells the compiler (
javac) that one instruction has ended.
Methods (Functions)
- A method performs a specific action.
- Methods can be predefined (like
System.out.print()) or user-defined. - We can pass data into methods called as arguments.
👉 Example here:
System.out.print("Hello java");
- Prints the string
"Hello java". -
"Hello java"is a string literal (just text).
Curly Braces { }
- Used for grouping code together into a block.
Classes
- In Java, everything lives inside a class.
-
Hellois our class name. - Convention: class names start with a capital letter.
💡 Important:
- If a class is declared
public, the filename must match the class name. - Public class →
Hello.java✅ - Non-public class → filename can be anything (but best practice is to match).
No matter what it will name bytecode file same as class name.
Remember:We compile files (
javac Hello.java)We run classes (
java Hello)
The main Method
public static void main(String[] args) { }
This is special in Java:
- Entry point of the program.
- Execution starts here.
- Must be public → JVM can access it.
- Must be static → JVM can call it without creating an object.
- void → no return value.
-
String[] args→ command-line arguments (will learn later).
👉 Without the main method, the program compiles fine, but the JVM can’t run it.
public, static, void — Quick Notes
-
public→ anyone can access it. -
static→ belongs to the class, not an object (deep dive later). -
void→ no return value.
🖥️ Running the Program
Compile the program
javac Hello.java
ls
Output:
Hello.java Hello.class
Run the program
java Hello
Output:
Hello java
⚡ Bonus: JShell
I also explored JShell, a REPL (Read–Eval–Print–Loop) included in JDK.
- Read → takes your input
- Evaluate → runs it
- Print → shows the result
- Loop → waits for more commands
👉 JShell is not an IDE. Its main purpose is quick testing, not for full development.
Example in JShell
jshell> System.out.println("Hello from JShell!");
Output:
Hello from JShell!
✨ Takeaway
- Wrote and ran my first Java program 🎉
- Got basic introduction to some keywords.
- Learned how to compile/run from terminal.
- Got introduced to JShell for quick testing.
Next up: For tomorrow, I will be doing front-end basics.🚀
Self notes
- I am happy that I am better than yesterday but it is long jouney ahead. Today day 2 I did my best with what time I got, as I was busy in some personal stuff. I wasted much time in choosing ide, later realising it doesn't matter. Somethings are better learned in hard way. I will be careful in future. Above notes are what I understand about the topics, they may be wrong. Thanks for reading.
This content originally appeared on DEV Community and was authored by Rohit Juyal
Rohit Juyal | Sciencx (2025-09-25T09:32:11+00:00) Hello Java. Retrieved from https://www.scien.cx/2025/09/25/hello-java/
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