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How to Download and Install Java 21

Java is one of the most popular programming languages in the world, used for developing applications for various platforms, such as desktops, web servers, mobile devices, embedded systems, etc. Java is also a platform-independent language, meaning that it can run on any machine that has a Java Virtual Machine (JVM) installed.

Java 21 is the latest release of the Java Standard Edition (SE) platform, which is scheduled to be released in September 2023 as a long-term support (LTS) release. This means that it will receive updates and security patches for several years after its release date. Java 21 introduces several new features and improvements that make Java more expressive, efficient, secure, and compatible.

In this article, we will show you how to download and install Java 21 on your computer, as well as how to use some of its new features. We will also explain why you should consider upgrading to Java 21 if you are still using an older version of Java.

System Requirements for Java 21

Before you download and install Java 21 , you should check if your system meets the minimum and recommended requirements for running Java 21. Here are the system requirements for Java 21 according to the official documentation:

Operating System	Minimum Requirement	Recommended Requirement
Windows	Windows 10 (64-bit)	Windows 10 (64-bit) with latest updates
Linux	Any Linux distribution that supports GLIBC 2.12 or later (64-bit)	Any Linux distribution that supports GLIBC 2.12 or later (64-bit) with latest updates
Mac OS	Mac OS X 10.13 or later (64-bit)	Mac OS X 10.15 or later (64-bit) with latest updates
Solaris	Solaris 11.4 or later (64-bit)	Solaris 11.4 or later (64-bit) with latest updates

In addition to the operating system, you also need to have enough memory and disk space to run Java 21. The minimum memory requirement is 128 MB of RAM, and the recommended memory requirement is 512 MB of RAM or more. The minimum disk space requirement is 250 MB of free space, and the recommended disk space requirement is 1 GB of free space or more.

Downloading Java 21

To download Java 21, you need to visit the official website of Oracle, which is the company that develops and maintains Java. You can find the download page for Java 21 here: https://www.oracle.com/java/technologies/downloads/

On this page, you will see different options for downloading Java 21, depending on your needs and preferences. Here are some of the options available:

• JDK (Java Development Kit): This is the option you should choose if you want to develop Java applications using Java 21. The JDK includes the Java compiler, the Java runtime, the JShell tool, and other development tools.
• JRE (Java Runtime Environment): This is the option you should choose if you only want to run Java applications using Java 21. The JRE includes only the Java runtime and does not include any development tools.
• GraalVM: This is an option you can choose if you want to use a high-performance JVM that supports multiple languages, such as JavaScript, Python, Ruby, etc. GraalVM is based on Java 21 and includes the JDK, the JRE, and other features.
• Eclipse Temurin: This is an option you can choose if you want to use a free and open-source distribution of Java 21 that is compatible with Oracle’s JDK. Eclipse Temurin is developed by the Eclipse Foundation and includes the JDK and the JRE.
• Zulu: This is an option you can choose if you want to use another free and open-source distribution of Java 21 that is compatible with Oracle’s JDK. Zulu is developed by Azul Systems and includes the JDK and the JRE.

You can choose any of these options depending on your needs and preferences, but for this article, we will assume that you are downloading the JDK from Oracle’s website. To do so, follow these steps:

1. Click on the “JDK Download” button on the download page.
2. Select your platform from the list of available platforms, such as Windows x64, Linux x64, Mac OS X x64, etc.
3. Accept the license agreement by checking the box next to it.
4. Click on the download link for your platform to start downloading the installer file.
5. Save the installer file to your preferred location on your computer.

Installing Java 21

To install Java 21 on your computer, you need to run the installer file that you downloaded in the previous step. The installation process may vary slightly depending on your platform, but in general, it involves these steps:

1. Double-click on the installer file to launch it.
2. Follow the instructions on the screen to complete the installation process.
3. Select a destination folder for installing Java 21 on your computer.
4. Select whether you want to install any additional features or tools, such as source code, demos, examples, etc.Click on the “Install” button to start the installation process.
5. Wait for the installation process to finish.
6. Click on the “Finish” button to exit the installer.

Congratulations, you have successfully installed Java 21 on your computer. You can verify that Java 21 is installed correctly by opening a command prompt or a terminal and typing the following command:

java -version 

You should see something like this:

java version "21" 2023-09-14 LTS Java(TM) SE Runtime Environment (build 21+12-LTS-237) Java HotSpot(TM) 64-Bit Server VM (build 21+12-LTS-237, mixed mode, sharing) 

How to Use Java 21

Now that you have installed Java 21 on your computer, you can start using it to develop and run Java applications. Java 21 comes with several tools and resources that can help you with your Java development. In this section, we will show you how to use some of these tools and resources.

Setting Up the Environment Variables

One of the first things you need to do before using Java 21 is to set up the environment variables that point to the Java 21 installation directory and bin folder. These environment variables are JAVA_HOME and PATH, and they are used by other tools and applications that rely on Java.

The JAVA_HOME environment variable is used to specify the location of the Java 21 installation directory on your computer. The PATH environment variable is used to specify the location of the Java 21 bin folder, which contains the executable files for the Java tools, such as javac, java, javadoc, etc.

The way you set up these environment variables depends on your operating system and platform. Here are some general steps for setting up these environment variables:

1. Find out the location of the Java 21 installation directory and bin folder on your computer. For example, if you installed Java 21 on Windows using the default settings, the installation directory would be C:\Program Files\Java\jdk-21, and the bin folder would be C:\Program Files\Java\jdk-21\bin.
2. Edit the system or user environment variables on your computer and add or modify the JAVA_HOME and PATH variables. For example, if you are using Windows, you can edit the environment variables by following these steps:
   • Open the Control Panel and click on System and Security.
   • Click on System and then click on Advanced system settings.
   • Click on Environment Variables.
   • In the System variables or User variables section, click on New to add a new variable, or click on Edit to modify an existing variable.
   • Enter JAVA_HOME as the variable name and enter the location of the Java 21 installation directory as the variable value. For example, C:\Program Files\Java\jdk-21.
   • Enter PATH as the variable name and enter the location of the Java 21 bin folder as the variable value. For example, C:\Program Files\Java\jdk-21\bin. If there are other values in the PATH variable, separate them with semicolons (;).
   • Click on OK to save the changes.
3. Restart your computer or open a new command prompt or terminal to apply the changes.

You can verify that the environment variables are set up correctly by typing the following commands in a command prompt or a terminal:

echo %JAVA_HOME% (for Windows) echo $JAVA_HOME (for Linux, Mac OS, or Solaris) java -version 

You should see something like this:

C:\Program Files\Java\jdk-21 (for Windows) /usr/lib/jvm/jdk-21 (for Linux, Mac OS, or Solaris) java version "21" 2023-09-14 LTS Java(TM) SE Runtime Environment (build 21+12-LTS-237) Java HotSpot(TM) 64-Bit Server VM (build 21+12-LTS-237, mixed mode, sharing) 

Using the Java Compiler and Runtime

The Java compiler and runtime are two of the most essential tools for using Java 21. The Java compiler is used to compile Java source code files into Java class files that can be executed by the JVM. The Java runtime is used to run Java class files or JAR files that contain Java applications.

The executable files for the Java compiler and runtime are javac and java respectively , and they are located in the Java 21 bin folder that you specified in the PATH environment variable. You can use these tools to compile and run Java programs from a command prompt or a terminal by following these steps:

1. Create a Java source code file with a .java extension that contains your Java program. For example, create a file named HelloWorld.java that contains the following code:

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

2. Open a command prompt or a terminal and navigate to the directory where you saved your Java source code file.
3. Type the following command to compile your Java source code file into a Java class file:

   javac HelloWorld.java 

   You should see a new file named HelloWorld.class in the same directory as your Java source code file.
4. Type the following command to run your Java class file using the Java runtime:

   java HelloWorld 

   You should see the output of your Java program on the screen. For example, you should see:

   Hello, world! 

You can use the same steps to compile and run any Java program using Java 21. You can also use some of the options and flags available for the javac and java commands to customize your compilation and execution process. For example, you can use the -d option for javac to specify the destination directory for the generated class files, or you can use the -cp option for java to specify the classpath for finding other class files or JAR files that your program depends on. You can find more information about the options and flags for javac and java here: https://docs.oracle.com/en/java/javase/21/docs/specs/man/javac.html and https://docs.oracle.com/en/java/javase/21/docs/specs/man/java.html

Using the JShell REPL Tool

The JShell tool is a new feature introduced in Java 9 that allows you to interactively evaluate Java expressions and statements without having to create a full Java program. JShell stands for Java Shell, and REPL stands for Read-Eval-Print Loop, which describes the process of reading user input, evaluating it as Java code, printing the result or error, and looping back to read more input.

The JShell tool is useful for testing, debugging, learning, and experimenting with Java code. You can use it to quickly try out new features in Java 21, such as string templates, record patterns, and unnamed patterns and variables. You can also use it to access existing Java classes and methods, as well as define your own variables, methods, classes, and interfaces.

The executable file for the JShell tool is jshell and it is located in the Java 21 bin folder that you specified in the PATH environment variable. You can use this tool to launch an interactive session of JShell by following these steps:

1. Open a command prompt or a terminal and type the following command:

   jshell 

   You should see something like this:

   |  Welcome to JShell -- Version 21 |  For an introduction type: /help intro jshell> 

2. Type any valid Java expression or statement at the prompt and press Enter. For example, type:

   System.out.println("Hello, JShell!"); 

   You should see something like this:

   Hello, JShell! jshell> 

3. To exit JShell, type:

   /exit 

   You should see something like this:

   |  Goodbye C:\> 

You can use various commands in JShell to control and customize your session. These commands start with a slash (/) and are not part of the Java language. For example, you can use the /help command to get help on using JShell, or you can use the /vars command to list all the variables that you have defined in your session. You can find more information about the commands available in JShell here: https://docs.oracle.com/en/java/javase/21/jshell/introduction-jshell.html#GUID-C337353B-074A-431C-993F-60C226163F00

Using the JavaP Decompiler

The JavaP decompiler is a tool that allows you to disassemble Java class files and inspect their contents. You can use it to view the bytecode instructions, the constant pool, the method signatures, the annotations, the attributes, and other information about the class files.

The JavaP decompiler is useful for debugging, learning, and reverse engineering Java code. You can use it to understand how the Java compiler translates your source code into bytecode, or to analyze the code of third-party libraries or applications that you do not have the source code for.

The executable file for the JavaP decompiler is javap and it is located in the Java 21 bin folder that you specified in the PATH environment variable. You can use this tool to decompile Java class files by following these steps:

1. Open a command prompt or a terminal and navigate to the directory where you have your Java class files.
2. Type the following command to decompile a Java class file:

   javap HelloWorld.class 

   You should see something like this:

   Compiled from "HelloWorld.java" public class HelloWorld {   public HelloWorld();   public static void main(java.lang.String[]); } 

3. To see more details about the class file, such as the bytecode instructions and the constant pool, you can use some of the options and flags available for javap. For example, you can use the -c option to print the disassembled code, or you can use the -v option to print the verbose output. You can find more information about the options and flags for javap here: https://docs.oracle.com/en/java/javase/21/docs/specs/man/javap.html

Using the JDeps Dependency Checker

The JDeps dependency checker is a tool that allows you to analyze the dependencies of Java class files and modules. You can use it to find out which classes or packages depend on which other classes or packages, or which modules depend on which other modules.

The JDeps dependency checker is useful for optimizing, modularizing, and migrating your Java code. You can use it to identify and eliminate unused or redundant dependencies, to split your code into smaller and more manageable modules, or to migrate your code from older versions of Java to newer versions of Java.

The executable file for the JDeps dependency checker is jdeps and it is located in the Java 21 bin folder that you specified in the PATH environment variable. You can use this tool to analyze the dependencies of Java class files and modules by following these steps:

1. Open a command prompt or a terminal and navigate to the directory where you have your Java class files or modules.
2. Type the following command to analyze the dependencies of a Java class file or module:

   jdeps HelloWorld.class 

   or

   jdeps hello.jar 

   You should see something like this:

   HelloWorld.class -> java.base    HelloWorld (HelloWorld.class)       -> java.io.PrintStream                   java.base       -> java.lang.Object                      java.base       -> java.lang.String                      java.base       -> java.lang.System                      java.base 

   or

   hello.jar -> java.base    com.example.hello (hello.jar)       -> java.io.PrintStream                   java.base       -> java.lang.Object                      java.base       -> java.lang.String                      java.base       -> java.lang.System                      java.base 

3. To see more details about the dependencies, such as the module graph, the package-level dependencies, or the JDK internal API dependencies, you can use some of the options and flags available for jdeps. For example, you can use the -m option to show the module-level dependencies, or you can use the -jdkinternals option to show the JDK internal API dependencies. You can find more information about the options and flags for jdeps here: https://docs.oracle.com/en/java/javase/21/docs/specs/man/jdeps.html

Using the JavaDoc Generator

The JavaDoc generator is a tool that allows you to generate HTML documentation from your Java source code. You can use it to create web pages that describe your classes, methods, fields, parameters, exceptions, annotations, etc., as well as any comments or tags that you have added to your source code.

The JavaDoc generator is useful for documenting, sharing, and maintaining your Java code. You can use it to create user-friendly and professional documentation for your own reference or for other developers who want to use your code. You can also customize your documentation by using different options and flags for the JavaDoc generator, such as the -d option to specify the destination directory for the generated HTML files, or the -stylesheet option to specify a custom CSS file for the HTML pages.

The executable file for the JavaDoc generator is javadoc and it is located in the Java 21 bin folder that you specified in the PATH environment variable. You can use this tool to generate HTML documentation from your Java source code by following these steps:

1. Open a command prompt or a terminal and navigate to the directory where you have your Java source code files.
2. Type the following command to generate HTML documentation from your Java source code files:

   javadoc *.java 

   You should see a new directory named doc in the same directory as your Java source code files. This directory contains the HTML files that document your Java code.
3. Open the index.html file in the doc directory with your web browser to view your documentation. You should see something like this:
4. To customize your documentation, you can use some of the options and flags available for javadoc. For example, you can use the -author option to include the author name in each HTML page, or you can use the -link option to link to external documentation sources. You can find more information about the options and flags for javadoc here: https://docs.oracle.com/en/java/javase/21/docs/specs/man/javadoc.html

Using the JAR Signer Utility

The JAR signer utility is a tool that allows you to sign and verify JAR files with digital signatures. You can use it to ensure the integrity and authenticity of your JAR files, as well as to grant them certain permissions or privileges when they are run by the JVM.

The JAR signer utility is useful for securing, distributing, and deploying your Java applications. You can use it to protect your JAR files from tampering or modification by unauthorized parties, to identify yourself or your organization as the source of your JAR files, and to enable your JAR files to access certain system resources or network connections that are otherwise restricted by the JVM.

The executable file for the JAR signer utility is jarsigner and it is located in the Java 21 bin folder that you specified in the PATH environment variable. You can use this tool to sign and verify JAR files by following these steps:

1. Open a command prompt or a terminal and navigate to the directory where you have your JAR file that you want to sign or verify.
2. Type the following command to sign a JAR file with a digital signature:

   jarsigner -keystore mykeystore.jks -storepass mypassword myjarfile.jar myalias 

   This command assumes that you have already created a keystore file named mykeystore.jks that contains your private key and public key certificate, and that you have specified a password for accessing your keystore file (mypassword) and an alias for identifying your key pair (myalias). You can create a keystore file using the keytool utility that is also located in the Java 21 bin folder. You can find more information about creating and managing keystores here: https://docs.oracle.com/en/java/javase/21/docs/specs/man/keytool.html
3. Type the following command to verify a JAR file with a digital signature:

   jarsigner -verify -verbose -certs myjarfile.jar 

   This command will check if the JAR file has been signed with a valid digital signature, and if so, it will display information about the signature, such as the signer’s name, certificate, and timestamp. You should see something like this:

   s k      1234 Thu Sep 23 12:34:56 PDT 2023 META-INF/MANIFEST.MF       [entry was signed on 9/23/23 12:34]       X.509, CN=John Doe, OU=Example Inc., O=Example Inc., L=San Francisco, ST=California, C=US       [certificate is valid from 9/1/23 12:00 AM to 9/30/23 12:00 AM]       [CertPath not validated: Path does not chain with any of the trust anchors] smk     5678 Thu Sep 23 12:34:56 PDT 2023 com/example/hello/HelloWorld.class       [entry was signed on 9/23/23 12: 34]       X.509, CN=John Doe, OU=Example Inc., O=Example Inc., L=San Francisco, ST=California, C=US       [certificate is valid from 9/1/23 12:00 AM to 9/30/23 12:00 AM]       [CertPath not validated: Path does not chain with any of the trust anchors] jar verified. 

4. To customize your signing and verification process, you can use some of the options and flags available for jarsigner. For example, you can use the -tsa option to specify a timestamp authority for your signature, or you can use the -keystore option to specify a different keystore file for your signature. You can find more information about the options and flags for jarsigner here: https://docs.oracle.com/en/java/javase/21/docs/specs/man/jarsigner.html

How to Try Out the New Features in Java 21

Java 21 introduces several new features that are in preview mode, meaning that they are not fully supported or standardized yet, but users can try them out by enabling them with a special flag. These features are intended to make Java more expressive, concise, and convenient for developers. In this section, we will show you how to try out some of these new features in Java 21.

String Templates (Preview)

String templates are a new feature that allows you to create formatted strings with placeholders that can be replaced with values at runtime. You can use string templates to avoid concatenating strings with the + operator or using the String.format method, which can be verbose and error-prone.

To create a string template, you need to use the $ symbol followed by an expression that evaluates to a value. For example, you can create a string template like this:

String name = "John"; String greeting = $"Hello, {name}!"; System.out.println(greeting); 

This will print:

Hello, John! 

You can also use expressions that involve operators, methods, or variables inside the placeholders. For example, you can create a string template like this:

int x = 10; int y = 20; String result = $"The sum of {x} and {y} is {x + y}."; System.out.println(result); 

This will print:

The sum of 10 and 20 is 30. 

To enable string templates in Java 21, you need to use the –enable-preview flag when compiling and running your Java code. For example, you can compile and run your code with string templates like this:

javac --enable-preview --release 21 HelloWorld.java java --enable-preview HelloWorld 

Record Patterns (Preview)

Record patterns are a new feature that allows you to deconstruct records into variables in switch expressions and statements. You can use record patterns to simplify and enhance your switch logic when dealing with records.

A record is a special kind of class that is introduced in Java 14 as a preview feature and finalized in Java 16. A record is used to define a data carrier class that has a fixed set of fields and methods. You can define a record like this:

record Point(int x, int y) {} 

This will automatically generate a constructor, getters, equals, hashCode, and toString methods for the record.

To use a record pattern in a switch expression or statement, you need to use the following syntax:

(recordType varName(fieldType fieldName)...) 

This will match any instance of the record type and assign its fields to the corresponding variables. For example, you can use a record pattern like this:

Point p = new Point(10, 20); switch (p) {     case Point(int x, int y) -> System.out.println($"The point has coordinates ({x}, {y}).");     default -> System.out.println("Not a point."); } 

This will print:

The point has coordinates (10, 20). 

To enable record patterns in Java 21, you need to use the –enable-preview flag when compiling and running your Java code. For example, you can compile and run your code with record patterns like this:

javac --enable-preview --release 21 HelloWorld.java java --enable-preview HelloWorld 

Unnamed Patterns and Variables (Preview)

Unnamed patterns and variables are a new feature that allows you to simplify pattern matching in switch expressions and statements. You can use unnamed patterns and variables to avoid repeating the same variable name or type in multiple cases, or to ignore the variable name or type altogether.

To use an unnamed pattern in a switch expression or statement, you need to use the following syntax:

(type _) 

This will match any instance of the type and ignore its value. For example, you can use an unnamed pattern like this:

Object obj = "Hello"; switch (obj) {     case String _ -> System.out.println("It's a string.");     case Integer _ -> System.out.println("It's an integer.");     default -> System.out.println("It's something else."); } 

This will print:

It's a string. 

To use an unnamed variable in a switch expression or statement, you need to use the following syntax:

(var _) 

This will match any value and ignore its type. For example, you can use an unnamed variable like this:

Object obj = "Hello"; switch (obj) {     case var _ -> System.out.println($"The object is {_}."); } 

This will print:

The object is Hello. 

To enable unnamed patterns and variables in Java 21, you need to use the –enable-preview flag when compiling and running your Java code. For example, you can compile and run your code with unnamed patterns and variables like this:

javac --enable-preview --release 21 HelloWorld.java java --enable-preview HelloWorld 

Conclusion

In this article, we have shown you how to download and install Java 21 on your computer, as well as how to use some of its new features. We have also explained why you should consider upgrading to Java 21 if you are still using an older version of Java.

Java 21 is the latest release of the Java SE platform, which is scheduled to be released in September 2023 as a long-term support (LTS) release. This means that it will receive updates and security patches for several years after its release date. Java 21 introduces several new features and improvements that make Java more expressive, efficient, secure, and compatible.

Some of the new features in Java 21 are in preview mode, meaning that they are not fully supported or standardized yet, but users can try them out by enabling them with a special flag. These features are intended to make Java more expressive, concise, and convenient for developers. Some of these features are string templates, record patterns, and unnamed patterns and variables.

If you want to learn more about Java 21 and its new features, you can visit the official website of Oracle here: https://www.oracle.com/java/technologies/downloads/. You can also find more resources and tutorials on Java 21 here: https://docs.oracle.com/en/java/javase/21/index.html.

FAQs

• Q: How can I download Java 21? A: You can download Java 21 from the official website of Oracle here: https://www.oracle.com/java/technologies/downloads/. You can choose from different options for downloading Java 21, such as JDK, JRE, GraalVM, Eclipse Temurin, or Zulu.
• Q: How can I install Java 21? A: You can install Java 21 by running the installer file that you downloaded from the official website of Oracle. The installation process may vary slightly depending on your platform, but in general, it involves selecting a destination folder, accepting the license agreement, and clicking on the install button.
• Q: How can I use Java 21? A: You can use Java 21 to develop and run Java applications using various tools and resources that come with Java 21. Some of these tools and resources are the Java compiler, the Java runtime, the JShell tool, the JavaP decompiler, the JDeps dependency checker, the JavaDoc generator, and the JAR signer utility.
• Q: How can I try out the new features in Java 21? A: You can try out some of the new features in Java 21 that are in preview mode by enabling them with a special flag when compiling and running your Java code. Some of these features are string templates, record patterns, and unnamed patterns and variables. You can find more information about these features and how to enable them here: https://docs.oracle.com/en/java/javase/21/language/index.html.
• Q: Why should I upgrade to Java 21? A: You should upgrade to Java 21 if you want to benefit from the latest features and improvements that make Java more expressive, efficient, secure, and compatible. Java 21 is also a long-term support (LTS) release, which means that it will receive updates and security patches for several years after its release date.

I hope you enjoyed this article and learned something new about Java 21. If you have any questions or feedback, please feel free to leave a comment below. Thank you for reading!

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