Java Hello World Program

In any programming language, a ‘Hello World‘ program is considered a simple program that outputs Hello, World! on the screen. It is often used to verify that the runtime environment is set up correctly and that we are ready to develop real-world applications.

In this Java tutorial, we will learn to write our first “Hello World” program in Java.

1. Hello World Program

The following program is the simplest Java program that prints the “Hello, World!” in the output console or prompt. It defines a class, HelloWorld. Note that the class name can be anything. We must ensure that the class is stored in a file with the same name.

public class HelloWorld {

    public static void main(String[] args) {

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

We can copy the above program and paste it directly into the editor. Still, I will recommend you write it yourself. This will help understand the difference in Syntax mainly the lower or upper case in keywords, classes, and methods.

Do not forget to save the Java file with name HelloWorld.java. In Java, a class name and the file (in which it is written) must be the same.

2. Compile and Run the Program

Java does not run the source files directly. We must compile the source .java file to .class file that JVM can understand and execute. Note that Java is case sensitive so make sure that the capitalization of the filename matches the class name. 

$ javac HelloWorld.java

The javac command will create the HelloWorld.class file in the same directory that contains the bytecode version of the program. Remember, bytecode is not executable code. Bytecode must be executed by a Java Virtual Machine.

Now we can execute the class file using the java command that uses the Java interpreter to run the program.

$ java HelloWorld.class

Notice the program has run and the output is displayed in the terminal. The program completes and ends immediately after printing the message as there is nothing to do in the program after this.

Hello, World!

Before moving on, it is important to mention that beginning with JDK 11, Java provides a way to run some types of simple programs directly from a source file, without explicitly invoking javac. But the limitation is that the program cannot use any external dependencies other than the java.base module. And the program can be only a single-file program.

$ java HelloWorld.java   //Prints Hello World!

3. How Does It Works?

Java is object oriented programming language. Everything in Java is encapsulated inside a Java class. In this case, the class name is HelloWorld.

The HelloWorld class contains the main() method which is the single starting point for JVM to start the execution of any program written in Java. Remember that we must provide the exact syntax of the main() method in the program which we want to execute.

public static void main(String[] args) { ... }

Let us note down a few important observations from this program:

• public means that all other classes can access it.
• static means that we can run this method without creating an instance of HelloWorld.
• void means that this method doesn’t return any value.
• main is the name of the method.
• String[] is the type that is used to refer to text content in Java. The [ ] brackets indicate that it is of array type.
• args is the name of the method argument, which is of type String[]. It means that the main method can accept multiple text inputs while starting the program execution. These arguments are generally user inputs to the program.
• System.out.println is the instruction given to JVM to print the given string Hello, World! to the console (default output target).

Happy Learning !!

Java Hello World Sourcecode