IT English Collection（27）of Collection

2024-05-03 16:32

文章标签 27 collection english

本文主要是介绍IT English Collection（27）of Collection，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

1 前言

本文主要介绍了Foundation中的collection（集合类），以及他们之间的区别和各自的特点。

转载请注明出处：http://blog.csdn.net/developer_zhang

2 详述

2.1 原文

A collection is a Foundation framework object whoseprimary role is to store objects in the form of arrays, dictionaries, and sets.

Collection Classes

The primary classes—NSArray, NSSet, and NSDictionary—share a number of features in common:

They can hold only objects, but the objects can be of any type. An instance of NSArray, for example, could contain cats, dogs, or wombats, or anycombination of these.
They maintain strong references to their contents.
They are immutable, but have a mutable subclass that allows you to change the contents of the collection.
You can iterate over their contents using NSEnumerator or fastenumeration.
Cocoa also provides three classes—NSPointerArray, NSHashTable, and NSMapTable—that aremodeled on these classes but that differ in the following ways:
·They may contain elements other than objects.
·They offer other memory management options.
·They are mutable.
Since a Cocoa collection object can hold any sort of object (unlike collections in some other environments), you typically don’t create special collection classes to contain objects of aparticular type.

Ordering Schemes
Collections store and vend other objects in a particular ordering scheme:
NSArray and its mutable subclass NSMutableArray use zero-based indexing.
In other environments, an array may be called a vector, table, or list.
NSPointerArray is modeled after NSMutableArray, but it can also hold NULL values (which contribute to the object’s count). You can also set the count of the pointer array directly (something you can’t do in atraditional array).

NSDictionary and its mutable subclass NSMutableDictionary use key-value pairs.
In other environments, a dictionary may be referred to as a hash table or hash map.

NSMapTable is modeled after NSMutableDictionary but provides different options, in particular to support weak relationships in agarbage-collected environment.

NSSet and its mutable subclass NSMutableSet provide unordered storage of objects.
Cocoa also provides NSCountedSet, which is a subclass of NSMutableSet and which keeps a count of how many times each object has been added to the set.