How to Fix java.lang.UnsupportedClassVersionError: A Complete Guide

Encountering the java.lang.UnsupportedClassVersionError is a common issue for Java developers. This error occurs when your Java Runtime Environment (JRE) is older than the version used to compile the class file. This guide explains why this error happens and provides step-by-step solutions to resolve it quickly.

Understanding the Error

The error message typically looks like this:

java.lang.UnsupportedClassVersionError: Unsupported major.minor version 65.0

The class file was compiled with a newer Java Development Kit (JDK) than the JRE version running it. For example, compiling with JDK 21 (class version 65) but running on JRE 17 (supports up to 61) will trigger this error.

Java Class File Version Compatibility

Each Java version has a unique major.minor version number:

Source: Oracle’s Java documentation.

How to Fix the Error

Update Your JRE/JDK

Your JRE is older than the JDK used to compile the class. Install the latest JRE/JDK matching the compilation version.

Check your current Java versions:

java -version   # Check JRE version
javac -version  # Check JDK version

Ensure both versions match.

Download and install the latest JDK from Oracle JDK or OpenJDK, selecting the version that matches your compiled class (e.g., JDK 21 for major version 65).

Set up environment variables:

Windows:

setx JAVA_HOME "C:\Program Files\Java\jdk-21"
setx PATH "%PATH%;%JAVA_HOME%\bin"

macOS/Linux:

export JAVA_HOME=/usr/lib/jvm/jdk-21
export PATH=$JAVA_HOME/bin:$PATH

Recompile with an Older Target Version

If updating the JRE is not possible, recompile the code to match the older JRE.

Using javac:

javac -target 1.8 -source 1.8 YourFile.java

Replace 1.8 with the required JRE version (e.g., 1.7 for Java 7).

Using build tools:

Maven:

<properties>
    <maven.compiler.source>1.8</maven.compiler.source>
    <maven.compiler.target>1.8</maven.compiler.target>
</properties>

Gradle:

java {
    sourceCompatibility = JavaVersion.VERSION_1_8
    targetCompatibility = JavaVersion.VERSION_1_8
}

Fix IDE-Specific Configurations

In Eclipse, go to Window > Preferences > Java > Compiler and set Compiler compliance level to match your JRE (e.g., 17 for Java 17).

In IntelliJ IDEA, navigate to File > Project Structure > Project Settings > Project, then set Project SDK and Project language level to the correct version.

Common Mistakes to Avoid

• JAVA_HOME should point to the correct JDK directory.
• PATH should include the JDK’s bin directory.
• Ensure both java (JRE) and javac (JDK) versions align.

Summary

By aligning your JDK (compile-time) and JRE (runtime) versions, you’ll eliminate the UnsupportedClassVersionError and ensure smooth execution of your Java applications.

Keywords: Fix UnsupportedClassVersionError, Java version mismatch, major.minor version error, update Java runtime, JDK JRE compatibility.