A05

Due Date: Friday, February 16
File(s) to be submitted: LinkedBag.java
Sample Output: SampleOutput.html
Starter Files:

• A05.java
• Bag.java
• LinkedBag.java

LinkedBag iterator (Chain-Based Implementations)

Summary

Complete the definition of the iterator method in the LinkedBag class. The implementation will require you to create a private class that implements the Iterator<E> interface.

Test your implementation using the A05 program provided.

Details

The sample implementation of LinkedBag is missing definitions for five methods. (Actually, there are definitions, but each one throws an UnsupportedOperationException.) You are to complete the definition of iterator (skip the other four).

The iterator method returns an Iterator<E>, where E is the base type of the Bag. (Thus, if it's a bag of Integer, the object returned will be an Iterator<Integer>; if it's a bag of String, the object returned will be an Iterator<String>.) But Iterator is an interface, so you'll need to create a class that implements that interface. Create a private class named LinkedBagIterator in your LinkedBag class.

The Iterator interface requires two methods:

• hasNext() -- which checks whether there are more elements to visit; and
• next() -- which returns the next element visited.

Note: you do not need to implement any other public methods in the Iterator interface. Those other methods (remove() and forEachRemaining(...)) have suitable default implementations.

You also should not implement any of the other ListIterator methods (such as previous and set). Those methods are not part of the Iterator interface.

There are two Exceptions that might be thrown by the methods in your private class.

• NoSuchElementException -- thrown by next() if the client tries to get data after the last element of the chain.
• ConcurrentModificationException -- thrown by next() and hasNext() if they notice that the size of the Bag has changed.

  If the size of the Bag changes, that means that an element has been added or removed, and under those circumstances the elements of the Bag might have moved (for a removal) or be where they're no longer reachable (for an add). In either case, there may now be elements in the Bag that the Iterator can't visit.

  Since the point of the iterator is to allow all elements of the Bag to be visited, that's a problem!

You should write a private method in your private class to check whether the size of the Bag has changed, and throw a ConcurrentModificationException if so.

Think about what information your Iterator object is going to need in order to do its job. Keep in mind that the LinkedBagIterator class is defined inside the LinkedBag class, so unless you make the private class static (don't do that), it'll have access to its Bag's instance variables.

Note

You won't need to use any of the methods defined in LinkedBag.

Do not modify any parts of LinkedBag other than the iterator method and the private class I'm asking you to create..