Java Versions and Release Cycle

Suppose your college lab has Java 8, a job description asks for Java 17, and a tutorial uses a feature from Java 21. Will your code work everywhere? It depends on the version, so you need to know how Java versions work.

Choosing the version also matters at work. A bank won't run its payment system on a version that stops getting security fixes in six months. That's why it picks an LTS version and upgrades from one LTS to the next.

Version Numbers

Older Java versions had confusing names. Java 5 was internally "1.5", and Java 8 still reports its version as 1.8.0_ followed by an update number. Since Java 9, version numbers are simple: 9, 10, 11 and so on, up to 25 and beyond.

A full version such as 25.0.2 means:

A New Release Every Six Months

Before 2018, there were often three or more years between versions: Java 7 came out in 2011, Java 8 in 2014 and Java 9 in 2017. Developers waited a long time for new features.

Starting with Java 10 in March 2018, Java moved to a fixed schedule: one feature release every March and every September. Each release is smaller, but you get improvements much sooner, and companies can plan their upgrades.

LTS and Feature Releases

Java 11 (2018) and Java 17 (2021) came three years apart. Since Java 17, an LTS version arrives every two years: Java 21 in September 2023 and Java 25 in September 2025. If the schedule continues, the next LTS will be Java 29 in September 2027. At the time of writing (November 2026), the newest release is Java 27, a feature release.

What Each LTS Version Added

Don't worry about these feature names now. Each one has its own lesson later in the course, and a summary lesson near the end brings them all together.

Preview Features

Sometimes a new feature appears as a preview first. It works, but it may still change, so you have to switch it on with the --enable-preview option. After feedback from developers, it becomes final in a later version. Pattern matching for switch, for example, was a preview in Java 17 to 20 and became final in Java 21.

Check the Version in Code

A program can check which Java version it is running on. This example tells you whether virtual threads (a Java 21 feature) are available.

public class VersionCheck {
    public static void main(String[] args) {
        int version = Runtime.version().feature();
        System.out.println("Java version: " + version);
 
        if (version >= 21) {
            System.out.println("Virtual threads are available.");
        } else {
            System.out.println("Use Java 21 or newer for virtual threads.");
        }
    }
}

Java version: 25
Virtual threads are available.

How it works

1. Line 3 reads the feature release number, such as 25, and stores it in version.
2. Line 4 prints it.
3. Line 6 compares it with 21. If the version is 21 or higher, the first message prints; otherwise the second one does. You'll learn if and else in "Java If-Else Statements".

The output above comes from Java 25. On another version, the first line shows that version.

Try it yourself: change 21 on line 6 to 30. Which message prints now, and why?

Common Mistakes

Learning Java 8 because it is "the one companies use". Many companies still run Java 8, but most new projects start on 17, 21 or 25. If you learn Java 25, you can still read Java 8 code, but a Java 8 course won't teach you records, var or virtual threads.

Using a feature release in production. A feature release such as Java 24 stopped getting updates when Java 25 came out. For anything that runs for a long time, choose an LTS version.

Mixing up compile and run versions. Code compiled with a newer Java may not run on an older JVM. If you compile with Java 25 and the server has Java 17, you'll see an UnsupportedClassVersionError.

Interview Corner

Practice

1. Easy: Write down which of these are LTS versions: 11, 14, 17, 20, 21, 24, 25.
2. Harder: Search for the Java version required by a framework you've heard of, such as Spring Boot. Is it an LTS version?

Key Takeaways