Cyclical dependency is not the right term. Static part of both class refers static member of the other.

Anyway, I use your pom.xml and I reproduce the problem with Oracle java 8 (maybe it depends on the order of class load):

$ cat src/main/java/JGModifierTypeIssue.java 

import org.janusgraph.graphdb.database.management.ModifierType;

public class JGModifierTypeIssue {

    public static void main(String[] args) {

        System.out.println(ModifierType.CONSISTENCY);

    }

}

$ mvn exec:java -Dexec.mainClass="JGModifierTypeIssue"

[INFO] Scanning for projects...

[INFO] 

[INFO] -----------------------< org.example:jgquestion >-----------------------

[INFO] Building jgquestion 1.0-SNAPSHOT

[INFO] --------------------------------[ jar ]---------------------------------

[INFO] 

[INFO] --- exec-maven-plugin:3.0.0:java (default-cli) @ jgquestion ---

[WARNING] 

java.lang.ExceptionInInitializerError

    at org.janusgraph.graphdb.database.management.ModifierType.<clinit> (ModifierType.java:23)

    at JGModifierTypeIssue.main (JGModifierTypeIssue.java:8)

    at org.codehaus.mojo.exec.ExecJavaMojo$1.run (ExecJavaMojo.java:254)

    at java.lang.Thread.run (Thread.java:748)

Caused by: java.lang.NullPointerException

    at org.janusgraph.graphdb.database.management.ModifierType.values (ModifierType.java:22)

    at org.janusgraph.graphdb.types.TypeDefinitionCategory.<clinit> (TypeDefinitionCategory.java:84)

    at org.janusgraph.graphdb.database.management.ModifierType.<clinit> (ModifierType.java:23)

    at JGModifierTypeIssue.main (JGModifierTypeIssue.java:8)

    at org.codehaus.mojo.exec.ExecJavaMojo$1.run (ExecJavaMojo.java:254)

    at java.lang.Thread.run (Thread.java:748)

[INFO] ------------------------------------------------------------------------

[INFO] BUILD FAILURE

[INFO] ------------------------------------------------------------------------

[INFO] Total time:  0.682 s

[INFO] Finished at: 2020-09-01T08:05:43+02:00

[INFO] ------------------------------------------------------------------------

[ERROR] Failed to execute goal org.codehaus.mojo:exec-maven-plugin:3.0.0:java (default-cli) on project jgquestion: An exception occured while executing the Java class. null: ExceptionInInitializerError: NullPointerException -> [Help 1]

[ERROR] 

[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.

[ERROR] Re-run Maven using the -X switch to enable full debug logging.

[ERROR] 

[ERROR] For more information about the errors and possible solutions, please read the following articles:

[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException

$ java -version

java version "1.8.0_201"

Java(TM) SE Runtime Environment (build 1.8.0_201-b09)

Java HotSpot(TM) 64-Bit Server VM (build 25.201-b09, mixed mode)

Regards,

Toom.

On Monday, August 31, 2020 at 9:31:30 PM UTC+2 HadoopMarc wrote:

Hi Thomas,

Thanks for asking on the user group first. I cannot reproduce the issue (works fine on my system using java8).

I ran:

    mvn exec:java -Dexec.mainClass="JGModifierTypeIssue"

and get CONSISTENCY printed whether the TypeDefinitionCategory line is commented out or not.

I used the pom.xml file below.

Also, java does not have the concept of cyclical dependencies (as in python): an import causes a class load unless the class is already loaded.

HTH,    Marc

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>

<groupId>org.example</groupId>
<artifactId>jgquestion</artifactId>
<version>1.0-SNAPSHOT</version>

<dependencies>
<dependency>
<groupId>org.janusgraph</groupId>
<artifactId>janusgraph-core</artifactId>
<version>0.5.2</version>
</dependency>
</dependencies>

<build>
<plugins>
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>exec-maven-plugin</artifactId>
<version>3.0.0</version>
<executions>
<execution>
<goals>
<goal>exec</goal>
</goals>
</execution>
</executions>
<configuration>
<executable>maven</executable>
</configuration>
</plugin>
</plugins>
</build>
</project>

Op maandag 31 augustus 2020 om 15:30:57 UTC+2 schreef Thomas Franco:

Hi,

When I try to set consistency of a property key (using JanusGraphManagement.setConsistency in a java project) I get a NPE if I don't refer the class TypeDefinitionCategory before.

The method setConsistency uses ModifierType and there is a cyclic dependency between  ModifierType  and TypeDefinitionCategory.

You can reproduce the error with this minimalist java code:

import org.janusgraph.graphdb.database.management.ModifierType;
import org.janusgraph.graphdb.types.TypeDefinitionCategory;

public class JGModifierTypeIssue {
  public static void main(String[] args) {

    TypeDefinitionCategory dummy = TypeDefinitionCategory.BACKING_INDEX; 
    // without the following line the next line generates a NPE
    System.out.println(ModifierType.CONSISTENCY);
  }
}

Should I create an issue on Github ?

Regards,

Toom.