### Question:
IndexPropertyList extends AbstractList implements ValueHolder { protected void sort() { if (!dirty) { return; } Collections.sort(unwrapList(), getComparator()); dirty = false; } IndexPropertyList(String indexProperty);  IndexPropertyList(String indexProperty, List objects, boolean sortNeeded); boolean isFault(); Object setValueDirectly(Object value); Object setValue(Object value); Object getValue(); Object getValueDirectly(); void invalidate(); void touch(); @Override Object get(int index); @Override int size(); @Override Object set(int index, Object element); @Override void add(int index, Object element); @Override Object remove(int index);  }### Answer:
@Test public void testSort() { IndexedObject o1 = new IndexedObject(1); IndexedObject o2 = new IndexedObject(2); IndexedObject o3 = new IndexedObject(3); IndexedObject o4 = new IndexedObject(4); List list1 = Arrays.asList(o2, o4, o3, o1); IndexPropertyList indexedList = new IndexPropertyList("order", list1, true); assertEquals(o1, indexedList.get(0)); assertEquals(o2, indexedList.get(1)); assertEquals(o3, indexedList.get(2)); assertEquals(o4, indexedList.get(3)); List list2 = Arrays.asList(o2, o4, o3, o1); IndexPropertyList indexedUnsortedList = new IndexPropertyList( "order", list2, false); assertEquals(o2, indexedUnsortedList.get(0)); assertEquals(o4, indexedUnsortedList.get(1)); assertEquals(o3, indexedUnsortedList.get(2)); assertEquals(o1, indexedUnsortedList.get(3)); }