cannot find symbol symbol: class Greet

[shaoshuaidu]

cannot find symbol symbol: class Greet

[johanandren]

If you must stay on JDK 8 the last version of Akka supporting it is 2.8.5, you could try building the quickstart with that.

[shaoshuaidu]

If you must stay on JDK 8 the last version of Akka supporting it is 2.8.5, you could try building the quickstart with that.

Hi Johanadren, thank you for your reply. Actually I am using Akka 2.8.5. Here is my pom file. Is there anyproblem with it?

4.0.0

<groupId>hello-akka-java</groupId>
<artifactId>app</artifactId>
<version>1.0</version>

<properties>
  <akka.version>2.8.5</akka.version>
</properties>

<repositories>
    <repository>
        <id>akka-repository</id>
        <name>Akka library repository</name>
        <url>https://repo.akka.io/maven</url>
    </repository>
</repositories>

<dependencies>
    <dependency>
        <groupId>com.typesafe.akka</groupId>
        <artifactId>akka-actor-typed_2.13</artifactId>
        <version>${akka.version}</version>
    </dependency>
    <dependency>
        <groupId>ch.qos.logback</groupId>
        <artifactId>logback-classic</artifactId>
        <version>1.2.13</version>
    </dependency>
    <dependency>
        <groupId>com.typesafe.akka</groupId>
        <artifactId>akka-actor-testkit-typed_2.13</artifactId>
        <version>${akka.version}</version>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.13.2</version>
        <scope>test</scope>
    </dependency>
</dependencies>
<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.8.1</version>
            <configuration>
                <source>1.8</source>    
                <target>1.8</target>
            </configuration>
        </plugin>
        <plugin>
            <groupId>org.codehaus.mojo</groupId>
            <artifactId>exec-maven-plugin</artifactId>
            <version>3.0.0</version>
            <configuration>
                <executable>java</executable>
                <arguments>
                    <argument>-classpath</argument>
                    <classpath />
                    <argument>$package$.AkkaQuickstart</argument>
                </arguments>
            </configuration>
        </plugin>
    </plugins>
</build>

[shaoshuaidu]

If you must stay on JDK 8 the last version of Akka supporting it is 2.8.5, you could try building the quickstart with that.

And my java version is 1.8 and maven version is 3.8.3. Should the version of maven be same as the version of maven compiler plugin?

[johanandren]

Ah, I see now what is wrong, you have probably cloned the entire java quickstart repository, but that is structured for project creation through the sbt (the build tool most common for Scala) templating functionality, not to be cloned and run directly.

Generally such project creation is done via sbt new akka/akka-quickstart-scala.g8, which will give you some prompts to specify project name, package name, Akka version etc.

If you do not want to install sbt to do that you can instead download a zip file of the project template from this page: https://developer.lightbend.com/guides/akka-quickstart-java/ and it should work as expected.

[shaoshuaidu]

Ah, I see now what is wrong, you have probably cloned the entire java quickstart repository, but that is structured for project creation through the sbt (the build tool most common for Scala) templating functionality, not to be cloned and run directly.

Generally such project creation is done via sbt new akka/akka-quickstart-scala.g8, which will give you some prompts to specify project name, package name, Akka version etc.

If you do not want to install sbt to do that you can instead download a zip file of the project template from this page: https://developer.lightbend.com/guides/akka-quickstart-java/ and it should work as expected.

Hi Johanandren,

Thank you for the information. Scala is an interesting and new language for me. But it seems not to be the reason of problem.

I finally found the bug is cuased by java version incompatibility. The code below (which is a record class, only supported by java 14 version and afterwards), is not supported by java 8.

public static record Greet(String whom, ActorRef<Greeted> replyTo) {}
 public static record Greeted(String whom, ActorRef<Greet> from) {}

So I change these code into typical class, and it works. Cheers!

public static final class Greet{
    private final String whom;
    private final ActorRef<Greeted> replyTo;

    public Greet(String whom, ActorRef<Greeted> replyTo){
      this.whom = whom;
      this.replyTo = replyTo;
    }

    public String whom(){
      return this.whom;
    }

    public ActorRef<Greeted> replyTo(){
      return this.replyTo;
    }

    public String toString(){
      return String.format("Point[x=%s, y=%s]", this.whom, this.replyTo);
    }

    public boolean equals(Object o){
      return true;
    }

    public int hashCode(){
      return 110;
    }
}

 public static final class Greeted{
    private final String whom;
    private final ActorRef<Greet> from;

    public Greeted(String whom, ActorRef<Greet> from){
      this.whom = whom;
      this.from = from;
    }

    public String whom(){
      return this.whom;
    }

    public ActorRef<Greet> from(){
      return this.from;
    }

    public String toString(){
      return String.format("Point[x=%s, y=%s]", this.whom, this.from);
    }

    public boolean equals(Object o){
      return false;
    }

    public int hashCode(){
      return 120;
    }
  }

[johanandren]

Ah, sorry, didn't remember that, yes, we switched to showcasing newer JDK features a while ago, if you start from commit akka/akka-quickstart-java.g8@269d369 I think that should still work with JDK 8 (alternatively rewrite those records to regular Java classes like you did)

[shaoshuaidu]

Ah, sorry, didn't remember that, yes, we switched to showcasing newer JDK features a while ago, if you start from commit akka/akka-quickstart-java.g8@269d369 I think that should still work with JDK 8 (alternatively rewrite those records to regular Java classes like you did)

Yeah, thanks. And I also create a new repo for java8 version, for new beginners like me. Here is the link https://github.com/shaoshuaidu/akka-quickstart-java8.

[johanandren]

Thanks for sharing, I'll close this issue now.