Use of AssertionError

Joshua Cranmer <Pidgeot18@verizon.invalid>
Sun, 30 Dec 2007 20:50:44 GMT
Having just read the
NullPointerException-IllegalArgumentException-AssertionError thread, I
was just wondering if my use of AssertionError in one case was valid.
This is a very pared-down interface of the code:

import java.util.*;

public final class ClassPool {
     public interface SourceHandler {
         public boolean hasClass(String name);

     private static List<SourceHandler> handlers =
         new LinkedList<SourceHandler>();

     static {
         // add a few handlers to the list...
         handlers.add(new SourceHandler() {
             public boolean hasClass(String name) {
                 return true;
         // This is not really an anonymous inner class, but it is the
         // best way for me to make it compilable

     // The user can add handlers but can never remove them.
     public static void addHandler(SourceHandler handler) {
         handlers.add(0, handler);

     // Edited for simplicity
     public static void getClass(String name) {
         for (SourceHandler handler : handlers) {
              if (handler.hasClass(name))
                  return; // Use this handler as the class
         // Since our last handler claims to handle everything, we should
         // never get here.
         throw new AssertionError();

Where I throw the assertion error explicitly, I want to put an `assert
false;' statement in (with a comment, of course), but then I would need
to insert a `return null;' at the end of the method, which would
invalidate the method contract which forbids null as a result but
assertions may not be on.

Is it more appropriate to put a RuntimeException or other type of error
instead of using an AssertionError here?
Beware of bugs in the above code; I have only proved it correct, not
tried it. -- Donald E. Knuth

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