Java - Hello World Program - Tech Guide Zone

Hello World Program

Here’s the simple Java program you can try:

HelloWorld.java

To Compile and Run (Using Terminal):

Save as HelloWorld.java
Open terminal or CMD and navigate to the file’s folder
Compile:
javac HelloWorld.java
Run:
java HelloWorld

Output:

Hello, Java!

Understanding the “Hello World” Java Program

When you begin learning any programming language, the first program you usually write is a Hello World program. It’s a simple example that introduces you to the basic structure and syntax of the language. Let’s go through a classic Java Hello World program step by step.

1. `public class HelloWorld`

class: In Java, everything revolves around classes. A class is like a blueprint for objects, and every piece of code must be inside a class.
HelloWorld: This is the class name. By convention, class names in Java start with a capital letter.
public: This is an access modifier. It means the class is accessible from anywhere in the program or outside it.

Note: The file name must match the class name.

So, if your class is named HelloWorld, the file should be saved as HelloWorld.java.

2. `public static void main(String[] args)`

This line is the entry point of every Java program. Let’s break down each part:

public: Means the method can be called from outside the class. The Java Virtual Machine (JVM) needs to access it, so it must be public.
static: Means this method belongs to the class, not an object. This way, the JVM can run the method without creating an object of the class.
void: This is the return type. void means the method does not return any value.
main: The name of the method. The JVM looks specifically for main as the starting point of a Java application.
String[] args: This is an array of Strings that can store command-line arguments. For example, if you run the program with:

java HelloWorld Welcome

Then args[0] will contain "Welcome".

Note: Without the main method, the program won’t run because the JVM won’t know where to start.

3. `System.out.println("Hello, Java!");`

This is the actual statement that prints text to the console.

System: A built-in class in Java’s standard library.
out: A static object of the PrintStream class, contained inside System. It represents the standard output stream (usually the console).
println: A method of PrintStream that prints the message passed to it and then moves the cursor to a new line.
"Hello, Java!": The text we want to display. Text enclosed in double quotes is called a string literal in Java.

Note: When you run this program, the output will be:

Hello, Java!

Complete Flow of Execution

The Java compiler (javac) compiles the HelloWorld.java file into HelloWorld.class (bytecode).
The JVM executes the bytecode, starting with the main method.
Inside the main method, it executes the statement System.out.println("Hello, Java!");.
The message Hello, Java! is displayed on the screen.

Key Points to Remember

Every Java program must have a class, and the file name should match the class name.
The main method is the starting point of the program.
System.out.println() is used to print messages to the console.
Java is case-sensitive: Main, main, and MAIN are all different identifiers.

Diagram – Structure of the Program

+—————————–+

| public class HelloWorld | <– Class definition

|—————————–|

| public static void main(…)| <– Entry point (main method)

| { |

| System.out.println(…); | <– Statement to print output

| } |

+—————————–+

This diagram shows how the program is divided into:

Class (HelloWorld)
Method (main)
Statement (System.out.println)

Execution Flow Diagram

With this program, you’ve taken your first step into Java programming. From here, you’ll build on these basics to learn variables, data types, loops, and object-oriented programming.