Avoid code duplication by using inheritance

I come from a C++ background where multiple inheritance is not a problem. Hoewever in Java I'm constrained to use either only class to inherit from or implement an interface. I have multiple classes that already extends another class. But all these classes should share the same debug interface/class. How do I implement such behaviour without duplicating my debug logic multiple times?

Consider my current setup:

public interface Debug
{
  public abstract void log();
}

public class ClassA extends AnotherBaseClass implements Debug
{
  public boolean doDebug = false;

  public void log()
  {
    if( doDebug )
      System.out.println( "LOG" );
  }
}

public class ClassB implements Debug
{
  public boolean doDebug = false;

  public void log()
  {
    if( doDebug )
      System.out.println( "LOG" );
  }
}