Each of the following three data structures, as written, cannot be changed once made (they are immutable). To use the editable versions, prepend Mutable before the class name: NSMutableString, NSMutableArray, NSMutableDictionary.
Stores objects in a list, fetching them by their position in the list, known as index.
Cannot store primitives. Resizes itself automatically.
AKA map, hash, associative array, keyed array.
Pairs keys to objects (like dictionary definitions paired to dictionary words).
No guarantees about the order of keys or objects within dictionary. Keys must implement Comparable (must be unique and comparable) by overriding equalTo: method. Strings are commonly used as keys. Cannot have duplicate keys (can have duplicate objects)
Wrapper class for strings. A collection of characters stored in order.
Literal strings are represented with
which can be assigned to any NSString variable.