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Java Hello World Tutorial | Advanced Java

First  Program | Hello World  | Java Tutorial

Overview

Java is a general-purpose programming language that focuses on the WORA (Write Once, Run Anywhere) principle.

It runs on a JVM (Java Virtual Machine) that is in charge of abstracting the underlying OS, allowing Java programs to run almost everywhere, from application servers to mobile phones.

When learning a new language, “Hello World” is often the first program we write.

In this tutorial, we’ll learn some basic Java syntax and write a simple “Hello World” program.

Conclusion

In this article, we talked about the Hello World program in Java.

We started by creating the program and then breaking it down to understand every line of code used to create the program.

We talked about classes, the

main

method, the

System.out.println()

statement, strings, and comments in Java.

Happy coding!

First  Program | Hello World  | Java Tutorial
First Program | Hello World | Java Tutorial

Object Oriented Programming

  • Java – OOPs Concepts
  • Java – Object & Classes
  • Java – Class Attributes
  • Java – Class Methods
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  • Java – Inner Classes
  • Java – Static Class
  • Java – Anonymous Class
  • Java – Singleton Class
  • Java – Wrapper Classes
  • Java – Enums

Advanced Java

  • Java – Command-Line Arguments
  • Java – Lambda Expressions
  • Java – Sending Email
  • Java – Applet Basics
  • Java – Documentation
  • Java – Autoboxing and Unboxing
  • Java – File Mismatch Method
  • Java – REPL (JShell)
  • Java – Optional Class
  • Java – Method References
  • Java – Functional Interfaces
How to Create Java Hello World Examples in Eclipse
How to Create Java Hello World Examples in Eclipse

Java Tutorial

  • Java – Home
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  • Java vs C++
  • Java Virtual Machine(JVM)
  • Java – JDK vs JRE vs JVM
  • Java – Hello World Program
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  • Java – Unicode System
  • Java – Basic Operators
  • Java – Comments

Java Useful Resources

  • Java Compiler
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  • Java – Examples

Java – Hello World Program

Printing “Hello World” on the output screen (console) is the first program in Java and other programming languages. This tutorial will teach you how you can write your first program (print “Hello World” program) in Java programming.

Java Tutorial Lesson 1 - Hello World
Java Tutorial Lesson 1 – Hello World

Java Error & Exceptions

  • Java – Exceptions
  • Java – try-catch Block
  • Java – try-with-resources
  • Java – Multi-catch Block
  • Java – Nested try Block
  • Java – Finally Block
  • Java – throw Exception
  • Java – Exception Propagation
  • Java – Built-in Exceptions
  • Java – Custom Exception

Steps to Write, Save, and Run Hello World Program

Let’s look at how to save the file, compile, and run the program. Please follow the subsequent steps −

  • Open notepad and add the code as above.
  • Save the file as − “MyFirstJavaProgram.java”.
  • Open a command prompt window and go to the directory where you saved the class. Assume it’s C:\.
  • Type ‘javac MyFirstJavaProgram.java’ and press enter to compile your code. If there is no error in your code, the command prompt will take you to the next line (Assumption − The path variable is set. Learn: Java Envionment Setup).
  • Now, type ‘java MyFirstJavaProgram’ to run your program.
  • You will be able to see “Hello World” printed on the screen.

Output

C:\> javac MyFirstJavaProgram.java C:\> java MyFirstJavaProgram Hello World

Java Hello World Example in Eclipse
Java Hello World Example in Eclipse

Writing the Hello World Program

Let’s open any IDE or text editor and create a simple file called HelloWorld.java:


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

In our example, we’ve created a Java class named HelloWorld containing a main method that writes some text to the console.

When we execute the program, Java will run the main method, printing out “Hello World!” on the console.

Now, let’s see how we can compile and execute our program.

Steps to Implement Java Program

Implementation of a Java application program involves the following step. They include:

  1. Creating the program
  2. Compiling the program
  3. Running the program

Creating Programs in Java

We can create a program using Text Editor (Notepad) or IDE (NetBeans)

class Test
{
public static void main(String []args)
{
System.out.println(“My First Java Program.”);
}
};

File Save: d:\Test.java

Compiling the Program in Java

To compile the program, we must run the Java compiler (javac), with the name of the source file on the “command prompt” like as follows

If everything is OK, the “javac” compiler creates a file called “Test.class” containing the byte code of the program.

Running the Program in Java

We need to use the Java Interpreter to run a program. Java is easy to learn, and its syntax is simple and easy to understand. It is based on C++ (so easier for programmers who know C++).

The process of Java programming can be simplified in three steps:

  • Create the program by typing it into a text editor and saving it to a file – HelloWorld.java.
  • Compile it by typing “javac HelloWorld.java” in the terminal window.
  • Execute (or run) it by typing “java HelloWorld” in the terminal window.

The below-given program is the most simple program of Java printing “Hello World” to the screen. Let us try to understand every bit of code step by step.

Very Simple Java Hello World program with Notepad and cmd ...
Very Simple Java Hello World program with Notepad and cmd …

Java Multithreading

  • Java – Multithreading
  • Java – Thread Life Cycle
  • Java – Creating a Thread
  • Java – Starting a Thread
  • Java – Joining Threads
  • Java – Naming Thread
  • Java – Thread Scheduler
  • Java – Thread Pools
  • Java – Main Thread
  • Java – Thread Priority
  • Java – Daemon Threads
  • Java – Thread Group
  • Java – Shutdown Hook

Conclusion

With this simple example, we created a Java class with the default main method printing out a string on the system console.

We saw how to create, compile, and execute a Java program and got familiar with a little bit of basic syntax. The Java code and commands we saw here remain the same on every OS that supports Java.

The Java Tutorials have been written for JDK 8. Examples and practices described in this page don’t take advantage of improvements introduced in later releases and might use technology no longer available.See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.

Now that you’ve seen the “Hello World!” application (and perhaps even compiled and run it), you might be wondering how it works. Here again is its code:

class HelloWorldApp { public static void main(String[] args) { System.out.println(“Hello World!”); // Display the string. } }

The “Hello World!” application consists of three primary components: source code comments, the

HelloWorldApp

class definition, and the

main

method. The following explanation will provide you with a basic understanding of the code, but the deeper implications will only become apparent after you’ve finished reading the rest of the tutorial.

The following bold text defines the comments of the “Hello World!” application:

/** * The HelloWorldApp class implements an application that * simply prints “Hello World!” to standard output. */ class HelloWorldApp { public static void main(String[] args) { System.out.println(“Hello World!”); // Display the string. } }

Comments are ignored by the compiler but are useful to other programmers. The Java programming language supports three kinds of comments:


/* text */


/*to


*/.


/** documentation */


/*and


*/. The


javadoctool uses doc comments when preparing automatically generated documentation. For more information on


javadoc, see the Javadoc™ tool documentation .


// text


//to the end of the line.


HelloWorldAppClass Definition

The following bold text begins the class definition block for the “Hello World!” application:

/** * The HelloWorldApp class implements an application that * simply displays “Hello World!” to the standard output. */ class HelloWorldApp { public static void main(String[] args) { System.out.println(“Hello World!”); // Display the string. } }

As shown above, the most basic form of a class definition is:

class name { . . . }

The keyword

class

begins the class definition for a class named

name

, and the code for each class appears between the opening and closing curly braces marked in bold above. Chapter 2 provides an overview of classes in general, and Chapter 4 discusses classes in detail. For now it is enough to know that every application begins with a class definition.


mainMethod

The following bold text begins the definition of the

main

method:

/** * The HelloWorldApp class implements an application that * simply displays “Hello World!” to the standard output. */ class HelloWorldApp { public static void main(String[] args) { System.out.println(“Hello World!”); //Display the string. } }

In the Java programming language, every application must contain a

main

method whose signature is:

public static void main(String[] args)

The modifiers

public

and

static

can be written in either order (

public static

or

static public

), but the convention is to use

public static

as shown above. You can name the argument anything you want, but most programmers choose “args” or “argv”.

The

main

method is similar to the

main

function in C and C++; it’s the entry point for your application and will subsequently invoke all the other methods required by your program.

The

main

method accepts a single argument: an array of elements of type

String

.

public static void main(String[] args)

This array is the mechanism through which the runtime system passes information to your application. For example:

java MyApp arg1 arg2

Each string in the array is called a command-line argument. Command-line arguments let users affect the operation of the application without recompiling it. For example, a sorting program might allow the user to specify that the data be sorted in descending order with this command-line argument:

-descending

The “Hello World!” application ignores its command-line arguments, but you should be aware of the fact that such arguments do exist.

Finally, the line:

System.out.println(“Hello World!”);

uses the

System

class from the core library to print the “Hello World!” message to standard output. Portions of this library (also known as the “Application Programming Interface”, or “API”) will be discussed throughout the remainder of the tutorial.

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When you’re learning a new programming language, you’ll often see the first program called a “Hello World” program. It’s used in most cases as a simple program for beginners.

I will assume that you’re either reading this article as a beginner to the Java programming language or you’re here to remember the good old Hello World program. Either way, it is going to be simple and straight to the point.

This article won’t only include the hello world program in Java, we’ll also talk about some terminologies you should know as a beginner learning to use Java.

To follow along, you’d need an integrated development environment (IDE). This is where you write and compile your code. You can install one on your PC or you can use any online IDE if you don’t want to go through with the installation process.

#0 Demo Kết Quả Đạt Được - Java Core | Khóa Học Java Cơ Bản Từ A tới Z cho Beginner
#0 Demo Kết Quả Đạt Được – Java Core | Khóa Học Java Cơ Bản Từ A tới Z cho Beginner

Java


class


HelloWorld {


public


static


void


main(String args[])


System.out.println(


"Hello, World"


);

The complexity of the above method

Time Complexity: O(1)

Space Complexity: O(1)

The “Hello World!” program consists of three primary components: the HelloWorld class definition, the main method, and source code comments. The following explanation will provide you with a basic understanding of the code:

Class Definition

This line uses the keyword class to declare that a new class is being defined.

class HelloWorld {
//
//Statements
}

HelloWorld

It is an identifier that is the name of the class. The entire class definition, including all of its members, will be between the opening curly brace “{” and the closing curly brace “}“.

main Method

In the Java programming language, every application must contain a main method. The main function(method) is the entry point of your Java application, and it’s mandatory in a Java program. whose signature in Java is:

public static void main(String[] args)

Explanation of the above syntax
  • public: So that JVM can execute the method from anywhere.
  • static: The main method is to be called without an object. The modifiers are public and static can be written in either order.
  • void: The main method doesn’t return anything.
  • main(): Name configured in the JVM. The main method must be inside the class definition. The compiler executes the codes starting always from the main function.
  • String[]: The main method accepts a single argument, i.e., an array of elements of type String.

Like in C/C++, the main method is the entry point for your application and will subsequently invoke all the other methods required by your program.

The next line of code is shown here. Notice that it occurs inside the main() method.

System.out.println(“Hello, World”);

This line outputs the string “Hello, World” followed by a new line on the screen. Output is accomplished by the built-in println( ) method. The System is a predefined class that provides access to the system and out is the variable of type output stream connected to the console.

Comments

They can either be multiline or single-line comments.

// This is a simple Java program.
// Call this file “HelloWorld.java”.

This is a single-line comment. This type of comment must begin with // as in C/C++. For multiline comments, they must begin from /* and end with */.

Important Points

  • The name of the class defined by the program is HelloWorld, which is the same as the name of the file(HelloWorld.java). This is not a coincidence. In Java, all codes must reside inside a class, and there is at most one public class which contains the main() method.
  • By convention, the name of the main class(a class that contains the main method) should match the name of the file that holds the program.
  • Every Java program must have a class definition that matches the filename (class name and file name should be same).

Compiling the Program

  • After successfully setting up the environment, we can open a terminal in both Windows/Unix and go to the directory where the file – HelloWorld.java is present.
  • Now, to compile the HelloWorld program, execute the compiler – javac, to specify the name of the source file on the command line, as shown:

javac HelloWorld.java

  • The compiler creates a HelloWorld.class (in the current working directory) that contains the bytecode version of the program. Now, to execute our program, JVM(Java Virtual Machine) needs to be called using java, specifying the name of the class file on the command line, as shown:

java HelloWorld

  • This will print “Hello World” to the terminal screen.

In Windows

In Linux

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First Java Program | Hello World Example

In this section, we will learn how to write the simple program of Java. We can write a simple hello Java program easily after installing the JDK.

To create a simple Java program, you need to create a class that contains the main method. Let’s understand the requirement first.

The requirement for Java Hello World Example

For executing any Java program, the following software or application must be properly installed.

Creating Hello World Example

Let’s create the hello java program:

Test it Now

Save the above file as Simple.java.

Output:

Hello Java

Compilation Flow:

When we compile Java program using javac tool, the Java compiler converts the source code into byte code.

Parameters used in First Java Program

Let’s see what is the meaning of class, public, static, void, main, String[], System.out.println().

To write the simple program, you need to open notepad by start menu -> All Programs -> Accessories -> Notepad and write a simple program as we have shownbelow:

As displayed in the above diagram, write the simple program of Java in notepad and saved it as Simple.java. In order to compile and run the above program, you need to open the command prompt by start menu -> All Programs -> Accessories -> command prompt. When we have done with all the steps properly, it shows the following output:

To compile and run the above program, go to your current directory first; my current directory is c:\new. Write here:

In how many ways we can write a Java program?

There are many ways to write a Java program. The modifications that can be done in a Java program are given below:

1) By changing the sequence of the modifiers, method prototype is not changed in Java.

Let’s see the simple code of the main method.

2) The subscript notation in the Java array can be used after type, before the variable or after the variable.

Let’s see the different codes to write the main method.

3) You can provide var-args support to the main() method by passing 3 ellipses (dots)

Let’s see the simple code of using var-args in the main() method. We will learn about var-args later in the Java New Features chapter.

4) Having a semicolon at the end of class is optional in Java.

Let’s see the simple code.

Valid Java main() method signature
Invalid Java main() method signature
Resolving an error “javac is not recognized as an internal or external command”?

If there occurs a problem like displayed in the below figure, you need to set a path. Since DOS doesn’t recognize javac and java as internal or external command. To overcome this problem, we need to set a path. The path is not required in a case where you save your program inside the JDK/bin directory. However, it is an excellent approach to set the path. Click here for How to set path in java.

Next TopicInternal details of Hello Java Program

Hello World Program in Java

In this section, we’ll create a simple Hello World program. We’ll then break it down so you’d understand how it works.

Here’s the code:


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

The code in the example above will print “Hello World!” in the console. This is commented out in the code. We’ll talk about comments shortly.

Let’s break down the code.

Classes in Java

Classes act as the building blocks for the overall application in Java. You can have separate classes for different functionalities.

Classes can also have attributes and methods that define what the class is about and what it does.

An example would be a Human class. It can have attributes like hair color, height, and so on. It can have methods like run, eat, and sleep.

In our Hello World program, we have a class called

HelloWorld

. As a convention, always start the name of your classes with an uppercase letter.

To create a class, you use the

class

keyword, followed by the name of the class. Here’s an example using our Hello World program:


class HelloWorld { }

The main Method in Java

Every Java program must have a

main

method. When the Java compiler starts executing our code, it starts from the

main

method.

Here’s what the

main

method looks like:


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

In order to keep this article simple, we won’t discuss other keywords found above like

public

,

static

, and

void

.

The System.out.println() Statement

We use the

System.out.println()

statement to print information to the console. The statement takes an argument. Arguments are written between the parentheses.

Here’s the syntax:


System.out.println(Argument)

In our case, we passed in “Hello World!” as an argument. You’ll notice that the text is surrounded by quotation marks. This tells the compiler that the argument is a

string

. Strings in programming are just a collection of characters – the same way we’d write regular text, but they must be in quotes.

Here’s what our code looks like:


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

When we run this code, “Hello World” will be printed.

It won’t be printed inside the code block above. I used

// Hello World!

as a way to show you the output of the code. That part of the code will not be executed by the compiler because it is a comment.

We use two forward slashes (

//

) to start a single line comment in Java.

Hello World in different programming languages #programming #memes
Hello World in different programming languages #programming #memes

Compiling and Executing the Program

In order to compile a Java program, we need to call the Java compiler from the command line:


$ javac HelloWorld.java

The compiler produces the HelloWorld.class file, which is the compiled bytecode version of our code.

Let’s run it by calling:


$ java HelloWorld

and see the result:


Hello World!

How Java “Hello, World!” Program Works?


  1. // Your First Program

    In Java, any line starting with

    //

    is a comment. Comments are intended for users reading the code to understand the intent and functionality of the program. It is completely ignored by the Java compiler (an application that translates Java program to Java bytecode that computer can execute). To learn more, visit Java comments.

  2. class HelloWorld { ... }

    In Java, every application begins with a class definition. In the program, HelloWorld is the name of the class, and the class definition is:

    class HelloWorld { … .. … }

    For now, just remember that every Java application has a class definition, and the name of the class should match the filename in Java.


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

    This is the main method. Every application in Java must contain the main method. The Java compiler starts executing the code from the main method.How does it work? Good question. However, we will not discuss it in this article. After all, it’s a basic program to introduce Java programming language to a newbie. We will learn the meaning of

    public

    ,

    static

    ,

    void

    , and how methods work? in later chapters.For now, just remember that the main function is the entry point of your Java application, and it’s mandatory in a Java program. The signature of the main method in Java is:

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


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

    The code above is a print statement. It prints the text


    Hello, World!

    to standard output (your screen). The text inside the quotation marks is called String in Java.

    Notice the print statement is inside the main function, which is inside the class definition.

Things to take away

  • Every valid Java Application must have a class definition that matches the filename (class name and file name should be same).
  • The main method must be inside the class definition.
  • The compiler executes the codes starting from the main function.

This is a valid Java program that does nothing.


public class HelloWorld { public static void main(String[] args) { // Write your code here } }

Don’t worry if you don’t understand the meaning of

class

,

static

, methods, and so on for now. We will discuss it in detail in later chapters.

Java is one of the most popular and widely used programming languages and platforms. Java is fast, reliable, and secure. Java is used in every nook and corner from desktop to web applications, scientific supercomputers to gaming consoles, cell phones to the Internet. In this article, we will learn how to write a simple Java Program.

Learn Java in 14 Minutes (seriously)
Learn Java in 14 Minutes (seriously)

Explanation of Hello World Program

As we’ve successfully printed Hello World on the output screen. Let’s understand the code line by line.

Public Main Class

public class MyFirstJavaProgram {

This line is creating a new class MyFirstJavaProgram and being public, this class is to be defined in the same name file as MyFirstJavaProgram.java. This convention helps Java compiler to identify the name of public class to be created before reading the file content.

Comment Section

/* This is my first java program. * This will print ‘Hello World’ as the output */

These lines being in /* */ block are not considered by Java compiler and are comments. A comment helps to understand program in a better way and makes code readable and understandable.

Public Static Void Main

public static void main(String []args) {

This line represents the main method that JVM calls when this program is loaded into memory. This method is used to execute the program. Once this method is finished, program is finished in single threaded environment.

Keywords Used

Let’s check the purpose of each keyword in this line.

  • public − defines the scope of the main method. Being public, this method can be called by external program like JVM.
  • static − defines the state of the main method. Being static, this method can be called by external program like JVM without first creating the object of the class.
  • void − defines the return type of the main method. Being void, this method is not returning any value.
  • main − name of the method
  • String []args − arguments passed on command line while executing the java command.

System.out.println() Method

System.out.println(“Hello World”); // prints Hello World

System.out represents the primary console and its println() method is taking “Hello World” as input and it prints the same to the console output.

By Pankaj

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Whenever we start to learn a programming language, the first program is always to print the Hello World. In the last article, we learned how to install Java on Windows 10. Now we are ready to write and run our first Hello World Java program.

To keep things simple and working for a new user, here is the sample hello world program that you can use.


public class JavaHelloWorldProgram { public static void main(String args[]){ System.out.println("Hello World"); } }

Save above program as

JavaHelloWorldProgram.java

in any directory.

Open Command Prompt and go to the directory where the hello world program file is saved. Then execute the below commands in order.


$javac JavaHelloWorldProgram.java $java JavaHelloWorldProgram Hello World

If you are using Java 11 or higher, then you can simply execute

java JavaHelloWorldProgram.java

and it will compile and execute the program for you. No need to explicitly compile and then run the java program.


JavaHelloWorldProgram.java


Class_Name.classextension. If you look at the directory where we compiled the java file, you will notice a new file created


JavaHelloWorldProgram.class


Exception in thread "main" java.lang.NoSuchMethodError: main.

I have recently created a short video for Java Hello World Program using Notepad and then Eclipse. Watch it for a better understanding. https://www.youtube.com/watch?v=ZREpFyjTDho That’s all for this post and you can start playing with your first class. In the next post, I will get into further details of classes, JDK, JVM, and other features provided by the Java programming language. Update: Read this post to know about JDK vs JRE vs JVM in java.

Thanks for learning with the DigitalOcean Community. Check out our offerings for compute, storage, networking, and managed databases.

public class ThankYou{ public static void main(String [] args){ System.out.println(“Thank you very much a good start form a beginner”); } }

– Adam

Thank you for amazing tutorials! Is it a good idea to add “how to create .exe / DMG / pkg” for this Hello World tutorial?

– Nik

i’m satisfied with this first topic

– Prakash Bale

excellent

– Sarawgi K

Excellent… But i have a question… If a public class is present in any java source file…why we should save the file name with the public class name??

– PRAVEEN KUMAR BADAM

Excelent

– Leandro

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