Question

I’m exposing an enumeration as a guide for traversing a tree-structure in preorder (an iterator uses these enum constants to decide how to traverse the tree):

/**
 * The result type of an {@link IVisitor} implementation.
 * 
 * @author Johannes Lichtenberger, University of Konstanz
 */
public enum EVisitResult {
  /** Continue without visiting the siblings of this node. */
  SKIPSIBLINGS,

  /** Continue without visiting the descendants of this node. */
  SKIPSUBTREE,

  /** Continue traversal. */
  CONTINUE,

  /** Terminate traversal. */
  TERMINATE,

  /** Pop from the right sibling stack. */
  SKIPSUBTREEPOPSTACK
}

However the last enum constant is only used for an internal visitor and shouldn’t ever be used from a user using the public API. Any ideas how I can hide “SKIPSUBTREEPOPSTACK”?

Answer 1

All you can do is document that it shouldn’t be used.

An alternative is to use an interface

public interface EVisitResult {
}

public enum PublicEVisitResult implements EVisitResult {
  /** Continue without visiting the siblings of this node. */
  SKIPSIBLINGS,

  /** Continue without visiting the descendants of this node. */
  SKIPSUBTREE,

  /** Continue traversal. */
  CONTINUE,

  /** Terminate traversal. */
  TERMINATE,
}

enum LocalEVisitResult implements EVisitResult {
  /** Pop from the right sibling stack. */
  SKIPSUBTREEPOPSTACK
}