The “Hello World” program is one of the simplest and most popular ways to introduce a programming language. In Java, this program demonstrates the structure of a Java application and serves as a basic starting point for beginners.


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.

Java Hello World Program

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., HelloWorldHelloWorld.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.

 

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