CIIT Institute | Learn Core Java Step-by-Step

Your First Java Program

Learn how to write, compile, and execute your first Java program using the standard Java application structure.

Writing Your First Java Program

A traditional Java application starts execution from the main() method. The following program prints a simple message to the console.

First Java Program

Java

public class FirstProgram {

    public static void main(String[] args) {

        System.out.println("Hello World CIIT....🌍!");

    }

}

Understanding the Program

Part	Explanation
`public`	An access modifier that makes the class or method accessible from other classes.
`class`	Defines a class in Java.
`FirstProgram`	The name of the class.
`static`	Allows the main method to be invoked without creating an object of the class.
`void`	Indicates that the method does not return a value.
`main()`	The traditional entry point of a Java application.
`String[] args`	Stores command-line arguments passed to the application.
`System.out.println()`	Prints a message followed by a new line.

Java File Naming Rule

When a class is declared as public, the source file name must match the public class name.

File

FirstProgram.java

The public class in this file is:

Java

public class FirstProgram

Compile the Program

Open a terminal in the directory containing FirstProgram.java and run:

Terminal

javac FirstProgram.java

If compilation succeeds, Java generates a bytecode file:

Generated File

FirstProgram.class

Run the Program

Execute the compiled class using the java command:

Terminal

java FirstProgram

Program Output

Output

Hello World CIIT....🌍!

Java Program Execution Flow

Flow

                    
                            FirstProgram.java
                                   ↓
                                 javac
                                   ↓
                            FirstProgram.class
                                   ↓
                                  JVM
                                   ↓
                                 main()
                                   ↓
                            System.out.println()
                                   ↓
                            Hello World CIIT....🌍!

Printing Different Values

Java can print strings, numbers, variables, and expressions.

Java

public class Main {

    public static void main(String[] args) {
        String instituteName = "CIIT Institute";
        String course = "Software Development";
        int version = 21;
        System.out.println("InstituteName: " + instituteName);
        System.out.println("Course: " + course);
        System.out.println("Version: " + version);
        System.out.println("2 + 3 = " + (2 + 3));

    }

}

Output

InstituteName: CIIT Institute
Course: Software Development
Version: 21
2 + 3 = 5

Java Comments

Comments are used to explain code and are ignored by the compiler.

Single-Line Comment

Java

// This is a single-line comment

System.out.println("CIIT....🤓❤️!");

Multi-Line Comment

Java

/*
    This is a
    multi-line comment.
*/

System.out.println("CIIT....🤓❤️!");

Common Beginner Mistakes

Forgetting the semicolon after a statement.
Using the wrong class name when running the program.
Saving a public class with a different file name.
Using java HelloWorld.java and java HelloWorld interchangeably without understanding the execution mode.
Forgetting to install or configure a JDK.

Important Points

Java source files normally use the .java extension.
The Java compiler is commonly invoked using javac.
Compiled bytecode normally uses the .class extension.
The JVM executes Java bytecode.
Traditional Java applications begin execution from main().

Summary

A basic Java program consists of a class and a main method. The source code is compiled into bytecode and executed by the JVM. Understanding this workflow is the foundation for learning Java programming.

← Previous: Development Tools Next: Basic Language →