How to solve “java.lang.UnsupportedClassVersionError”


What is java.lang.UnsupportedClassVersionError?

The java.lang.UnsupportedClassVersionError is a runtime error in Java that occurs when you try to run a class file compiled with a higher version of Java than what is currently installed or supported by the Java Virtual Machine (JVM). This error indicates a version mismatch between the compiled Java bytecode and the JVM.

The java.lang.UnsupportedClassVersionError error occurs when the major version of the compiled Java class file is higher than the major version supported by the Java Virtual Machine (JVM) running the program.

For example, let's say you compiled your Java class file using Java SE 11 (major version 55) and then try to run it on a JVM that only supports Java SE 8 (major version 52). In this case, you would encounter the UnsupportedClassVersionError because the major version of the class file (55) is not compatible with the JVM (52).


Here are the major and minor version numbers for the different versions of Java:

1.             Java SE 1.1 - Major version: 45, Minor version: 3

2.             Java SE 1.2 - Major version: 46, Minor version: 0

3.             Java SE 1.3 - Major version: 47, Minor version: 0

4.             Java SE 1.4 - Major version: 48, Minor version: 0

5.             Java SE 5 (Java 5) - Major version: 49, Minor version: 0

6.             Java SE 6 (Java 6) - Major version: 50, Minor version: 0

7.             Java SE 7 (Java 7) - Major version: 51, Minor version: 0

8.             Java SE 8 (Java 8) - Major version: 52, Minor version: 0

9.             Java SE 9 (Java 9) - Major version: 53, Minor version: 0

10.         Java SE 10 (Java 10) - Major version: 54, Minor version: 0

11.         Java SE 11 (Java 11) - Major version: 55, Minor version: 0

12.         Java SE 12 (Java 12) - Major version: 56, Minor version: 0

13.         Java SE 13 (Java 13) - Major version: 57, Minor version: 0

14.         Java SE 14 (Java 14) - Major version: 58, Minor version: 0

15.         Java SE 15 (Java 15) - Major version: 59, Minor version: 0

16.         Java SE 16 (Java 16) - Major version: 60, Minor version: 0

17.         Java SE 17 (Java 17) - Major version: 61, Minor version: 0

Please note that the major and minor version numbers represent the format of the class file generated by the Java compiler and are not necessarily related to the versioning scheme of the Java Development Kit (JDK).

It's important to ensure that the major version of the class file aligns with the major version supported by the JVM to avoid the UnsupportedClassVersionError and successfully run the Java application.


Reasons for the error:

1.    JVM version mismatch: The class file was compiled with a higher Java version than the one installed on the system running the JVM.

 

·       Verify the Java version: Check the version of Java installed on the system by running java -version in the command prompt/terminal.

·       Compile with a compatible Java version: If the Java version used during development is higher than the one installed, recompile the source code with the appropriate Java version. For example, if the JVM is Java 8, compile the code with Java 8.

·       Upgrade or install Java: If the JVM version is older, consider upgrading to a higher version of Java or installing the required version.

 

2.    Incompatible Java versions: The class file was compiled with a Java version that is not compatible with the targeted JVM version.

Specify the target Java version: If you're using a build tool like Maven or Gradle, ensure that the target Java version is set correctly in the project configuration. For example, in Maven's pom.xml, you can set the target version with the following configuration:

<build>

    <plugins>

        <plugin>

            <groupId>org.apache.maven.plugins</groupId>

            <artifactId>maven-compiler-plugin</artifactId>

            <configuration>

                <source>1.8</source> <!-- Source code compatibility -->

                <target>1.8</target> <!-- Target JVM version -->

            </configuration>

        </plugin>

    </plugins>

</build>

Use cross-compilation options: If you need to compile the code with a higher version of Java while maintaining compatibility with an older JVM, you can use cross-compilation options provided by the compiler. For example, to compile code for Java 8 while running on Java 7, you can use the -source and -target options:

javac -source 1.8 -target 1.7 MyClass.java

3.    Deployment environment inconsistency: The application is being deployed to an environment with a different JVM version than what was used during development.

·       Check the JVM version on the deployment environment: Ensure that the JVM version installed on the deployment environment matches the version used during development and compilation

·       Provide the required JVM version: If the deployment environment has an older JVM version, consider upgrading it to a compatible version or provide instructions for users to install the required JVM version.

By ensuring the compatibility of the Java versions and the JVM used for compilation and execution, you can resolve the java.lang.UnsupportedClassVersionError and run the Java application successfully.