Compiler Error J0198

An enclosing instance of type 'identifier' is required

The compiler detected that an inner class definition tried to reference something outside of its scope. Examples of when this can occur are:

• A class declared within another class as static referenced one of the parent class's non-static variables or methods. Since the inner class is declared static it cannot reference any members of the parent class without an instance of the parent class defined.
  
  
• An inner class tried to reference a class that was not its outer class using the this keyword with the classes name preceding it. Since the referenced class is not the inner class's parent class, an instance cannot be implied.

The following examples illustrate this error:

//This example illustrates the first error situation
public class Simple{
   int x = 10;
   static class InnerClass{
      public void method1(){
         int y = x; /*error: instance variable needed
                             to reference parent
                             variables. */
      }
   }
}

//This example illustrates the second error situation
class A{
   int x;
}
class B{
   //Do something meaningful here
   class InnerClass{
      void method1(){
         int y = A.this.x;
         /*error: no instance of A defined. Cannot use
           the <classname.this.variable> syntax here.*/
      }
   }
}