With Java 8's "default method" feature, any abstract class without direct or inherited field should be converted into an interface.

Note that this rule is automatically disabled when the project's sonar.java.source is lower than 8.

Noncompliant Code Example

public abstract class Car {
  public abstract void start(Environment c);

  public void stop(Environment c) {
    c.freeze(this);
  }
}

Compliant Solution

public interface Car {
  public void start(Environment c);

  public default void stop(Environment c) {
    c.freeze(this);
  }
}