UnsupportedClassVersionError : Error with Gradle and Java Runtime version

Question

I'm very new to Gradle, and I wanted to give a try to this cool project : Strange, a Quantum Computing API for Java (I'll leave a link to the github project below). They recommend using Gradle, so I did.

In the directory I'm working on, there's only 3 files :

1. My java main class HelloStrangeWorld.java,
2. build.gradle,
3. and settings.gradle

Now I just wanted to test, in my directory, the command :

$ gradle tasks

And I got this :

FAILURE: Build failed with an exception. * What went wrong: java.lang.UnsupportedClassVersionError: org/javamodularity/moduleplugin/ModuleSystemPlugin has been compiled by a more recent version of the Java Runtime (class file version 55.0), this version of the Java Runtime only recognizes class file versions up to 52.0

org/javamodularity/moduleplugin/ModuleSystemPlugin has been compiled by a more recent version of the Java Runtime (class file version 55.0), this version of the Java Runtime only recognizes class file versions up to 52.0

---

What I have :

• My Java is set on 1.8

• I installed Graddle using SDKMAN

The content of build.gradle is the following :

plugins {
    id 'java'
    id 'application'
    id 'org.javamodularity.moduleplugin' version '1.2.1'
}

group 'helloStrangeWorld'
version '1.0-SNAPSHOT'

repositories {
    mavenCentral()
}

dependencies {
    testCompile group: 'junit', name: 'junit', version: '4.12'
    compile 'com.gluonhq:strange:0.0.5'
}

mainClassName = 'HelloStrangeWorld'

The content of my main class is the following :

import com.gluonhq.strange.*;
import com.gluonhq.strange.gate.*;
import com.gluonhq.strange.local.SimpleQuantumExecutionEnvironment;
import java.util.Arrays;

public class HelloStrangeWorld {

    public static void main(String[] args) {
        Program p = new Program(2);
        Step s = new Step();
        s.addGate(new X(0));
        p.addStep(s);
        Step t = new Step();
        t.addGate(new Hadamard(0));
        t.addGate(new X(1));
        p.addStep(t);
        SimpleQuantumExecutionEnvironment sqee = new SimpleQuantumExecutionEnvironment();
        Result res = sqee.runProgram(p);
        Qubit[] qubits = res.getQubits();
        Arrays.asList(qubits).forEach(q -> System.out.println("qubit with probability on 1 = "+q.getProbability()+", measured it gives "+ q.measure()));
    }

}

What I've tried so far :

• I have checked that my JAVA_HOME is setted to my jdk8. I use zsh, so I checked on both .bashrc and .zshrc, and the env variable is setted in both place.

• I changed from Java 8 to Java 7, it returns me that Gradle isn't supposed to work with Java 7. So I went back to Java 8

• I checked the symbolic links setted in /etc/alternatives and all the java related are pointing to the version 8 of java

Am I missing something obvious about the use of Gradle ?

Thank you

Here's the link for the Strange project on gitHub.

Answer 1

Java 8 doesn't support quantum computing. You need Java 11 or later.

Jokes aside, the project you're including depends on OpenJFX 11-ea+24, which requires Java 11.

Get OpenJDK 11 here.

Note: UnsupportedClassVersionError prints a number like 55.0. Subtract 44 from it to determine the needed Java version.