// file A.java
package foo;
public abstract class A { public abstract void service(int i);}

// file B.java
package foo;
public abstract class B extends A { // without "abstract" modifier, it's ok 
      protected void service(char c) {} // without service(char), it works, too
      public void service(int i) {}
}

// file C.scala
package foo;
class C extends B {}