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Web context: How To Write Your First Program in Java | DigitalOceanBlogDocsGet SupportContact SalesDigitalOceanProductsFeatured ProductsDropletsScalable virtual machinesKubernetesScalable virtual machinesAI / MLBuild and scale AI modelsCloudwaysManaged cloud hostingApp PlatformGet apps to market fasterComputeDropletsKubernetesCPU-Optimized DropletsFunctionsApp PlatformAI / MLGPU DropletsGenAI PlatformBackups & SnapshotsBackupsSnapshotsSnapShooterNetworkingVirtual Private Cloud (VPC)Cloud FirewallsLoad BalancersDNSDDoS ProtectionManaged DatabasesMongoDBKafkaMySQLPostgreSQLCachingOpenSearchStorageSpaces Object StorageVolume Block StorageDeveloper ToolsAPICLISupport PlansMonitoringUptimeIdentity Access ManagementCloud Website HostingCloudwaysSee all productsSolutionsAI and Machine LearningDevelop, train, and deploy AI appsGPUsNotebook IDEBlockchainInfrastructure for decentralized appsBlogs, Forums and Content WebsitesLightning-fast, reliable CMS hostingWordpressGhostMastodonData AnalyticsReal-time data processing at scaleData StreamingAdTech & MartechDeveloper ToolsDevOps and CI/CD solutionsCI/CDPrototypingDigital Marketing AgenciesPower your clients’ websites and campaignsFreelancerIT ConsultingEcommerceBuild beautiful online storefrontsDropshippingWooCommerceMagentoGame DevelopmentLow-latency multiplayer serversMinecraft HostingIOTConnect to the power of the cloudISVsStreamlined ISV application developmentSecure Web HostingPowerful protection from DDoS and morePrivate VPNStartup Cloud HostingScalable, cost-effective infrastructureSmall BusinessVideo StreamingHigh-bandwidth, low-latency deliveryWeb and Mobile AppsSimple cross-platform app hostingcPanelDockerNext.jsNode.jsWebsite HostingFast page loads and reliable site uptimeVPS HostingVirtual MachinesQuestions?Talk to an expertSee all solutionsDevelopersOur CommunityCommunity HomeDevOps and development guidesCSS-TricksAll things web designThe WaveContent to level up your business.ResourcesTutorialsQuestions and AnswersMarketplaceToolsWrite for DOnationsCustomer StoriesDigitalOcean BlogPricing CalculatorGet InvolvedHatch Startup ProgramOpen Source SponsorshipsHacktoberfestDeploy 2024DO ImpactNonprofitsDocumentationQuickstartComputeStorageManaged DatabasesContainersBillingAPI ReferencePartnersDigitalOcean Partner ProgramsBecome a PartnerPartner Services ProgramISV Partner ProgramMarketplaceHatch Partner ProgramConnect with a PartnerPartner Programs ResourcesCustomer StoriesDigitalOcean Onboarding SeriesTraining for Agencies and FreelancersPrice Estimate CalculatorFeatured Partner ArticlesCloud cost optimization best practicesRead moreHow to choose a cloud providerRead moreDigitalOcean vs. AWS Lightsail: Which Cloud Platform is Right for You?Read moreQuestions?Talk to an expertPricingLog inLog in to:CommunityDigitalOceanSign upSign up for:CommunityDigitalOceanBlogDocsGet SupportContact SalesLog inLog in to:CommunityDigitalOceanSign upSign up for:CommunityDigitalOceanTutorialsQuestionsLearning PathsFor BusinessesProduct DocsSocial ImpactSearch CommunityCONTENTSPrerequisitesWriting and Executing the “Hello, World!” Program in JavaUnderstanding the “Hello, World!” ProgramCompiling and Running the “Hello, World!” ProgramConclusionTutorial Series: How To Code in Java1/9 How To Write Your First Program in Java2/9 Understanding Data Types in Java3/9 How To Use Operators in Java4/9 How To Write Conditional Statements in Java5/9 How To Use Loops in Java6/9 How To Use Arrays in Java7/9 How To Use Lists in Java8/9 How To Use Maps in Java9/9 How to Use Lambdas in JavaTutorialHow To Write Your First Program in JavaPublished on September 16, 2022DevelopmentJavaToliandRachel LeeThe author selected theFree and Open Source Fundto receive a donation as part of theWrite for DOnationsprogram.IntroductionJavais a mature and well-designed programming language with a wide range of uses, from being studied in class to running commercial applications of any size. One of its unique benefits is that it is cross-platform: once you create a Java program, you can run it on many operating systems, including servers (Linux/Unix), desktop (Windows, macOS, Linux), and mobile operating systems (Android, iOS).Java achieves high performance because it executes compiled (that is, machine-optimized) code. For developers, this means that you have to compile its source code before you can run it. If you’re used to languages such as PHP and Python, which allow source code to be executed directly, then compiling the code first will be a new step in the development process.In this tutorial, you’ll create a “Hello, World!” program in Java. The “Hello, World!” program is a classic and time-honored tradition in computer programming. It’s a complete first program for beginners, and it’s a good way to make sure your environment is properly configured. By creating a “Hello, World” program, you’ll start learning Java’s basic syntax as well as the compilation and execution process of a Java program. Once you’re finished, you’ll be able to write and run basic Java code.PrerequisitesFor this tutorial, you will need:Java (version 11 or above) installed on your machine. For Ubuntu and Debian, follow the steps for Option 1 in our tutorial,How To Install Java with Apt on Ubuntu 22.04. For other operating systems, including Mac and Windows, see thedownload options for Java installation.A compiler provided by the Java Development Kit (JDK). To compile the source code, you’ll use the default Java compiler calledjavac. You can compile your source either on your local computer or on a remote server in the cloud. For Ubuntu, you can follow the JDK installation instructions in Option 1 fromHow To Install Java with Apt on Ubuntu 22.04. For other platforms, see Oracle’sJDK Installation Guideorthe official instructions for installing OpnJDKversion 11 or above.(Optional) A Java Runtime Environment (JRE) that will execute the compiled code. The JRE is part of the JDK, so you don’t have to install it additionally if you have already installed the JDK. Otherwise, you can install the JRE separately. This can be useful if you intend to run your code on a remote server where you don’t want to compile code for security reasons. In this kind of server-oriented scenario, you can download and install the JRE via the native package manager. For Ubuntu and Debian, usesudo apt install openjdk-11-jre. For other distributions, use the respective package managers and search for the keywordjreand choose version 11 or above.A terminal in which to execute commands. Java is well supported on all major operating systems, which means you can follow the instructions on your local computer and use a terminal to connect to a remote server. For guidance on connecting to remote servers, follow ourInitial Server Setup Guide.A text editor such asnano. To get started writing Java code, you can use any text editor. However, to code efficiently, consider using an integrated development environment (IDE), such asEclipse IDE. IDEs are useful because they correct your syntax, autocomplete your code, and allow you to test the code directly, saving you the manual compilation step. However, IDEs are not always intuitive and may confuse you if you haven’t used them before. For your first Java program, it may be easier to use the text editor you are used to.Writing and Executing the “Hello, World!” Program in JavaFor many people, their first Java program is often also their last Java program. The problem is that even the simplest code seems too complex and you have to learn quite a few new things to fully understand it. To avoid this common pitfall, you’ll begin by writing the code, running it, and then seeing how it works.To get started, create a new directory calledhello-worldin which to place the code for this tutorial. To create a project directory and change into it, run the following commands in a terminal:mkdirhello-worldcdhello-worldNext, usingnanoor your favorite text editor, create a file calledHello.java. Fornano, use the following command:nanoHello.javaAdd the following code to your file. It is the bare minimum code for printing a “Hello, World!” message to the console.hello-world/Hello.javapublicclassHello{publicstaticvoidmain(String[]args){System.out.println("Hello, World!");}}This program will print the messageHello, World!to the console. The file name (in this case,Hellowith the extension.java) has to match the name of the public class in the source code, which isHello. Matching the file name and public class name in the source code is a convention of Java. (This is helpful to remember because if you find some useful code, you’ll know how to name the Java source code file.)Save and close your file. Usingnano, pressCTRL+Xto exit,Yto save, andENTERto confirm the filename and close the file.In your terminal, runjavacfrom the same directory where theHello.javafile is located so that the code is compiled:javac Hello.javaThe source Java code has to be compiled usingjavacwith the full file name.Finally, execute the program with thejavaexecutable like this:javaHelloTo execute the compiled code, you have to runjavafollowed by the name of the class (which isHelloin this example). You cannot use any file name extension such as.javaor.classwhen executing the code.Your output will look like this:OutputHello, World!Your program ran successfully! You created a basic Java program, compiled it, and executed it. Next, you’ll see how it all works.Understanding the “Hello, World!” ProgramIf you’re used to writing code in Python or JavaScript, you’ll find that Java has some differences, even in a small program. Every Java program needs at least two things:A class for your code.A main method inside your class.You need a class because Java isobject-oriented, and all code must be a part of a class.Classesare functionally related code. Usually, they do not function on their own but instead serve as templates from which objects are created. Anobjectis a specific instance of a class that can be used within your code. Objects have properties and are able to act when you trigger their methods.In your program, the class isHello:hello-world/Hello.javapublicclassHello{publicstaticvoidmain(String[]args){System.out.println("Hello, World!");}}The first line of the code denotes the start of a class. Classes always start withclassfollowed by their name. In this case, the name of the class isHello, and it matches the name of the file with the.javaextension. Then there is an opening curly bracket ({) and a closing curly bracket (}) at the end of the code snippet, inside which you put the code of the class.The class has an access modifier (which methods also have). In this case, it ispublic, which means it is fully accessible.It’s a best practice to use only one class per file, which makes the code easier to read. Still, there is no such official requirement, and you can have an unlimited number of classes inside one single file. There is one catch, though—only one of the classes inside a file can be public, and it should have the same case-sensitive name.In addition to a class, your program also has a main method. Themain methodis the starting point of execution for a class—and for this tutorial, for the whole program. It has a very specific syntax:public static void main(String[] args):hello-world/Hello.javapublicclassHello{publicstaticvoidmain(String[]args){System.out.println("Hello, World!");}}publicis the access modifier and means that there are no restrictions on calling the method.staticis a special keyword denoting that the method (in this case) or property does not require a new object to be created explicitly in order for you to be able to call it. This has many uses; in particular, it resolves a possible “chicken and egg” situation in which, at some point, some code should be able to create the first object of your program without being part of an object itself.voidis the return type, and it means that nothing is being returned to the caller. In this case, you’ll be printing a message to the screen and thus directly consuming the result of the execution. Althoughvoiddoesn’t return anything here, in other cases, methods often return a variety of information, such as alphanumeric characters, integers, or objects.String[] argsis the parameter or the input for themainmethod. A string of characters, orstring, stores alphanumeric information. The square brackets ([]) indicate that it’s an array of strings and not only one string. The name of this array isargs. In this case,main()doesn’t have any arguments, but if there were any, they’d be contained in this array.If you miss any of the main method attributes, such as the fact that it ispublic, you may not get a syntax error, but it will not work as intended (as a starting point).To print the text to the console, you use the methodSystem.out.println():hello-world/Hello.javapublicclassHello{publicstaticvoidmain(String[]args){System.out.println("Hello, World!");}}A method tells the computer to perform an action. We can tell it is a method because it uses parentheses:(). The method itself isprintln()and accepts one argument for the text to be printed.System.outprecedes the method to specify that the method is part of the core Java (System) functionality for output (out).In this case, you are using a method from the subpackageout, which is part of the parent package,System. To get a better idea of how classes are organized in Java, imagine that the class hierarchy is similar to that of a file system with parent folders and related dependent subfolders. In Java, these folders are referred to aspackages. Related classes are put in one package or subpackage depending on how granular the hierarchy is.The argument toSystem.out.println()is a string:"Hello, World!". We know it’s a string because a string is always surrounded by double quotes. In contrast to other languages, such as PHP, single quotes cannot be used for Java strings.One peculiarity of Java syntax is that it requires a semicolon at the end of each statement, such as the one for printing the text:System.out.println("Hello, world!");.Note:If you’re using an IDE or a text editor with Java syntax support, you don’t need to worry about missing semicolons because these programs automatically take care of this and other syntax quirks.In this section, you examined your program line-by-line to understand how it works. In the next section, you’ll take a look at what happens when you compile and run the program.Compiling and Running the “Hello, World!” ProgramIn this section, you’ll review what happens when you compile and run your Java program. To compile the code, you usedjavacfrom theJDK:javac Hello.javajavacwill read the source code, check it for syntax errors, apply optimizations, and produce a byte code file calledHello.class. AJava.classfile is the machine code that the JRE is able to interpret and run.You can view theHello.classfile by running thelscommand from the project directory.lsThis command lists the files in your current directory:OutputHello.classHello.javaAfter the code is compiled, you run it with thejavaexecutable from theJRE:javaHelloThe JRE runs only compiled code and is not able to execute code from a standard human-readable file in any way. Similarly, if you try to read a compiled.classfile with a standard text editor, you won’t be able to. Though, with the help of tools such as theJava Decompiler, you are able to read compiled files, which can be useful when debugging programs for which you don’t have the source code.With this command, you instruct the JRE executablejavato process a class calledHello, which is found in theHello.classfile.When theHello, World!message prints to the console, you have confirmed the following:You have a correctly working Java environment in which you are able to compile and execute code.Java has successfully located the code for theHelloclass, and it is able to access it.The execution flow started from themain()method. There, the methodSystem.out.println()has been invoked with the string argumentHello, World!. The welcome message has been printed on the screen.Since there is no other code, the program successfully exited.By invokingjava, you start a type of virtual machine called aJava virtual machine(JVM). Check out our article,What is a Virtual Machine?for more general information on virtual machines.The JVM is well-isolated with no dependencies on the external environment, libraries, or the hosting operating system as a whole. The JVM behaves very similarly, if not exactly the same, on different operating systems, which makes Java portable, predictable, and secure. This is in contrast to other languages such as PHP, where the PHP interpreter relies on many native libraries from the operating system.Because Java runs its own virtual machine to achieve such isolation, that process consumes quite a few megabytes of memory. However, Java is optimized to manage resources efficiently. Even with the resource consumption involved in running its own virtual machine, Java has excellent performance for large, complex, and long-running programs.In other words, there may be more easier or more efficient ways to program messages that print to the screen in other languages. But by using Java, you will be well-positioned to create complex programs that are compatible with various operating systems.ConclusionCongratulations! You have written your first Java program.You can continue playing with the code in theHello.javafile and see what happens when you change the text or when you remove the semicolon and get an error. Just make sure to compile the code (javac Hello.java) every time you make changes to theHello.javafile.For more on Java, check out ourHow To Code in Javaseries.Thanks for learning with the DigitalOcean Community. Check out our offerings for compute, storage, networking, and managed databases.Learn more about our productsNext in series: Understanding Data Types in Java ->Tutorial Series:How To Code in JavaJava is a mature and well-designed programming language with a wide range of uses. One of its unique benefits is that it is cross-platform: once you create a Java program, you can run it on many operating systems, including servers (Linux/Unix), desktop (Windows, macOS, Linux), and mobile operating systems (Android, iOS).SubscribeDevelopmentJavaBrowse Series: 9 articles1/9 How To Write Your First Program in Java2/9 Understanding Data Types in Java3/9 How To Use Operators in JavaExpand to view allAbout the authorsToliauthorRachel LeeeditorTechnical EditorStill looking for an answer?Ask a questionSearch for more helpWas this helpful?YesNoCommentsLeave a comment﻿This textbox defaults to usingMarkdownto format your answer.You can type!refin this text area to quickly search our full set oftutorials, documentation & marketplace offerings and insert the link!Sign In or Sign Up to CommentThis work is licensed under a Creative Commons Attribution-NonCommercial- ShareAlike 4.0 International License.Try DigitalOcean for freeClick below to sign up and get$200of creditto try our products over 60 days!Sign upPopular TopicsAI/MLUbuntuLinux BasicsJavaScriptPythonMySQLDockerKubernetesAll tutorialsTalk to an expertJoin the Tech TalkSuccess!Thank you! 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User: Can you write me a step by step guide to code in Java with sample code blocks in it
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