title: Could not find implementation class for plugin error when using plugin “java-gradle-plugin”
body: <p>Gradle 4.10.2</p>
  
  <p>NOTE: I posted the same question in the Gradle Forum page but have had 0 traction after 1 week.</p>
  
  <p>I’ve read <a href="https://discuss.gradle.org/t/could-not-find-implementation-class-for-plugin-error-when-using-gradle-4-1/24279" rel="nofollow noreferrer">Could not find implementation class for plugin error when using Gradle 4.1+</a> but I may have a different issue, but I’m not sure.</p>
  
  <p>This is my first time writing a plugin so I’m just following <a href="https://guides.gradle.org/writing-gradle-plugins/" rel="nofollow noreferrer">Writing Gradle Plugins</a> tutorial, and <a href="https://docs.gradle.org/4.10.3/userguide/java_gradle_plugin.html" rel="nofollow noreferrer">Gradle Plugin Development Plugin</a>.</p>
  
  <p>Here’s my plugin’s <code>build.gradle</code> file</p>
  
  <pre><code>apply plugin: 'java'
  apply plugin: 'java-gradle-plugin'
  
  gradlePlugin {
      plugins {
          simplePlugin {
              id = 'org.example.greeting.greeting-plugin'
              implementationClass = 'org.example.greeting.GreetingPlugin'
          }
      }
  }
  </code></pre>
  
  <p>However when I get this when I build</p>
  
  <pre><code>$ ./gradlew clean build
  
  **&gt; Task :jar**
  
  :jar: A valid plugin descriptor was found for org.example.greeting-plugin.properties but the implementation class org.example.greeting.GreetingPlugin was not found in the jar.
  
  **BUILD SUCCESSFUL** in 0s
  </code></pre>
  
  <p>How can I fix it?</p>