Java Hello World Program

Code: Java Hello World

// HelloWorld.java
public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

Explanation of the Code

1. // HelloWorld.java:

   • This is a comment in Java. Comments are ignored by the compiler and are used to explain code.

2. public class HelloWorld:

   • A class is the blueprint for an object in Java.
   • public makes the class accessible from anywhere.
   • HelloWorld is the name of the class, and it must match the filename (HelloWorld.java).

3. public static void main(String[] args):

   • This is the entry point of every Java application. The JVM starts execution from the main method.
   • public: The method is accessible from anywhere.
   • static: The method belongs to the class rather than an object.
   • void: The method does not return any value.
   • String[] args: This parameter stores command-line arguments passed to the program.

4. System.out.println("Hello, World!");:

   • This prints the text Hello, World! to the console.
   • System.out: Represents the standard output stream.
   • println: Prints the string and moves the cursor to the next line.

Steps to Run the Program

1. Write the Code:

   • Open a text editor or an IDE (like Eclipse, IntelliJ IDEA, or VS Code).
   • Save the file as HelloWorld.java.

2. Compile the Program:

   • Open a terminal or command prompt.
   • Navigate to the folder containing HelloWorld.java.
   • Run the command:

     
     javac HelloWorld.java
     

   • This compiles the Java file into a bytecode file named HelloWorld.class.

3. Run the Program:

   • Execute the program using the JVM with the command:

     
     java HelloWorld
     

   • You should see the output:

     
     Hello, World!
     

Common Errors

1. Filename Mismatch:

   • The class name must match the filename (e.g., HelloWorld → HelloWorld.java).
   • If the names do not match, you will get an error like:

     
     Error: Could not find or load main class HelloWorld
     

2. Missing Semicolon:

   • Java statements end with a semicolon (;). Forgetting it will cause a compilation error.

3. Case Sensitivity:

   • Java is case-sensitive. Ensure that method and class names use the correct capitalization.

Variations of Hello World

1. Using Variables:

   
   public class HelloWorld {
       public static void main(String[] args) {
           String message = "Hello, World!";
           System.out.println(message);
       }
   }
   

2. Adding User Input:

   
   import java.util.Scanner;
   
   public class HelloWorld {
       public static void main(String[] args) {
           Scanner scanner = new Scanner(System.in);
           System.out.print("Enter your name: ");
           String name = scanner.nextLine();
           System.out.println("Hello, " + name + "!");
       }
   }
   

Key Takeaways

• Java programs start execution from the main method.
• A compiled Java program generates a .class file, which the JVM executes.
• Java’s simplicity and clear syntax make it beginner-friendly.