Implementing abstract list
java
Solution
You are not overriding the method `add()`.
The javadoc for AbstractList states:
Note that this implementation throws an UnsupportedOperationException unless add(int, Object) is overridden.
The fix is... to override the method. Or not use the `add()` method so your `MyArrayList`'s size is immutable (but not it's values) - like an array, which is what you're storing your values in.
Problem
I was looking at the http://docs.oracle.com/javase/tutorial/collections/custom-implementations/index.html tutorial and I tried to do the same : ``` class MyArrayList<T> extends AbstractList<T> { private final T[] a; MyArrayList(T[] array) { a = array; } @Override public T get(int index) { return a[index]; } @Override public T set(int index, T element) { T oldValue = a[index]; a[index] = element; return oldValue; } @Override public int size() { return a.length; } @Override public Object[] toArray() { return (Object[]) a.clone(); } public static void main(String[] args) { String[] arr = {"one", "two", "three"}; MyArrayList<String> list = new MyArrayList<String>(arr); list.get(1); list.add(1, "seven"); System.out.println(list); } } ``` I get an exception while trying to insert the element : ``` Exception in thread "main" java.lang.UnsupportedOperationException at java.util.AbstractList.add(Unknown Source) ``` Why is that, how do I fix it?