Chapter 4, lesson1: Collecting Data Items.

• collections - classes used for grouping, managing, iterating over related objects.
• challenge - to discern the right colln to use in a specific situation.

ArrayList

• A simple, resizeable, unordered, index-based colln of objs of any type.
• adding/removing items - designed for these operations.
• adding - can add objects that exist as variabls, created inline, and even value types. Value types will implicitly firstly be wrapped in a obj ref. - i.e. boxed.
• AddRange - adding from an array or another collection. Supports adding a range of items from any object that supports ICollection interface.
• Add/AddRange - add to end of ArrayList.
• Insert/InsertRange - insert at specific positions.
• Use Indexer to set at a position - however not same as Insert - it overwrites.
• Remove, RemoveRange, RemoveAt.
• Contains, IndexOf, Clear - if Contains(myString), then IndexOf(myString), RemoveAt(index) else Clear().

ArrayList - iterating

There are several mths to iterate over items in an ArrayList.

• numeric indexer - for x = 0 to colln.Count - colln[x]
• IEnumerable - ArrayList supports this interface which allows use of Enumerator to access list - GetEnumerator() returns an IEnumerator interface, which provides mechanism - MoveNext() - for iterating in fwd direction.
• IEnumerator - colln.GetEnumerator(); while(enum.MoveNext()) - enum.Current;
• foreach - enumerates a colln. Can be used on any colln that support IEnumerable.

Interfaces in Collections

• ICollection - derived from IEnumerable - implemented in the API of most colln classes.
• ICollection.CopyTo - easy way to copy contents -> Array.
• IList - derived from ICollection - exposes mthds to get at items.

Sorting - colln.Sort();

Sort works by using Comparer class to perform comparison.

Comparer class - default implementation that supports IComparer interface.

IComparer - impl. Compare() - takes 2 objs & returns an int that represents the result.

Sort - allows one to specify diff obj which implements IComparer.