throwing exceptions in Iterator subclasses

The java Iterator class is defined as follows:

Code:

---

public interface Iterator<E> {

        boolean hasNext();

    /**
    * Returns the next element in the iteration.
    *
    * @return the next element in the iteration.
    * @exception NoSuchElementException iteration has no more elements.
    */
    E next();

        void remove();
}

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the comment for E next() states that subclasses will throw NoSuchElementException if the collection has no more elements. How can subclasses throw this exception when E next() has no throws declaration? My understanding of Java exception handling reuires a throws declaration on next(). Please help me to understand.

The NoSuchElementException API docs describe its parentage as follows:

Code:

---

java.lang.Object
  extended by java.lang.Throwable
      extended by java.lang.Exception
          extended by java.lang.RuntimeException
              extended by java.util.NoSuchElementException

---

Runtime exceptions don't have to be declared like other sorts of exception. Another runtime exception is the NullPointerException which we all know (to our cost) can be thrown in all sorts of methods regardless of their throws declaration.

Sun's Tutorial discusses the so-called unchecked exceptions in the section Unchecked Exceptions - The Controversy. The advice given there is "If a client can reasonably be expected to recover from an exception, make it a checked exception. If a client cannot do anything to recover from the exception, make it an unchecked exception."

Also - and perhaps better - you may want to check out what the tutorial has to say about The Catch or Specify Requirement.

THanks for the info. The tutorial is very informative.

You're welcome. And welcome to the Forums! If anything there provokes a specific question (or observation), then post away. (or if my brief reference to RuntimeException wasn't enough of an answer to your original question)