How to Check Java Version

Introduction

Before we begin talking about how to check Java version, let's briefly understand – What is Java?

Java is a popular programming language known for its versatility and portability. Created by Sun Microsystems, now owned by Oracle, Java is widely used in web development, mobile apps, and enterprise software.

Its key features include object-oriented programming, automatic memory management, and "write once, run anywhere" capability, allowing code to be executed on different platforms without modification. Java's wide adoption and vast community support make it an excellent choice for developers aiming for scalable and robust applications.

This tutorial outlines how to find out what version of Java is installed on your Linux system using the command line. This is useful for installing applications that require a specific version of Java.

Advantages of Java

1. Portability: Java's "write once, run anywhere" ability allows code to be used on various platforms.
2. Object-Oriented: It supports OOP principles, enabling modular and organized programming.
3. Robust & Secure: Built-in safety features and error handling ensure reliable and secure applications.
4. Versatile: Used for web, mobile, enterprise, and more, making it adaptable for various development needs.
5. Huge Community & Libraries: A vast community and extensive libraries offer abundant resources and support for developers.

Java Versioning

Java employs semantic versioning. The following versioning scheme is used for production-ready releases:

MAJOR.MINOR.SECURITY

In Java 11.0.8, for instance, 11 is the major version, 0 is the minor version, and 8 is the security version.

• MAJOR - Major releases include new features and functions.
• MINOR - Minor releases include various bug fixes and compatible improvements.
• SECURITY - Security releases contain essential security fixes.

Checking Java Version

To find out the version of Java is installed on your machine, simply run the java -version command:

java -version

The command will print the default Java version:

Output

openjdk 11.0.8 2020-07-14
OpenJDK Runtime Environment (build 11.0.8+10-post-Ubuntu-0ubuntu120.04)
OpenJDK 64-Bit Server VM (build 11.0.8+10-post-Ubuntu-0ubuntu120.04, mixed mode, sharing)

In this example, our machine is running Java 11.0.8. It is possible that the version installed on your system is different.

If you receive the error message “java: command not found,” Java is not installed on your system. Depending on your Linux distribution, use one of the following guides to install Java:

• Install Java on Ubuntu.
• Install Java on Debian.
• Install Java on CentoS.

The system may even have numerous versions of Java installed at the same time. Run the following command to see if your system has multiple Java installations:

sudo update-alternatives --config java

If you only have one Java installation, the output will be as follows:

Output

There is only one alternative in link group java (providing /usr/bin/java): /usr/lib/jvm/java-11-openjdk-amd64/bin/java
Nothing to configure.

Otherwise, the command will show a menu where you can choose which version will be the default Java version if you have multiple Java installations:

Output

There are 3 choices for the alternative java (providing /usr/bin/java).

  Selection    Path                                            Priority   Status
------------------------------------------------------------
* 0            /usr/lib/jvm/java-11-openjdk-amd64/bin/java      1111      auto mode
  1            /usr/lib/jvm/java-11-openjdk-amd64/bin/java      1111      manual mode
  2            /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java   1081      manual mode

Press <enter> to keep the current choice[*], or type selection number:

Type the version number (the number in the Selection column) and press Enter to change the default Java version.

FAQs to Check Java Version

Conclusion

You can easily find out what Java version is installed on your Linux system by typing java -version.

If you have any queries, feel free to drop a comment below, and we'll be happy to help.