NSMutableArray类
    The NSMutableArray class declares the programmatic interface to objects that manage a modifiable array of objects. This class adds insertion and deletion operations to the basic array-handling behavior inherited from NSArray.

NSMutableArray类，声明可编程接口，用于管理对象的可变数组。这个类在继承NSArray类的基础数组操作方法上，新增添加和修改操做。

方法：
    insertObject:atIndex:
    removeObjectAtIndex:
    addObject:
    removeObject:
    removeLastObject
    replaceObjectAtIndex:withObject:

NSUserDefaults类
    The NSUserDefaults class provides a programmatic interface for interacting with the defaults system. The defaults system allows an application to customize its behavior to match a user’s preferences. For example, you can allow users to determine what units of measurement your application displays or how often documents are automatically saved. Applications record such preferences by assigning values to a set of parameters in a user’s defaults database. The parameters are referred to as defaults since they’re commonly used to determine an application’s default state at startup or the way it acts by default.

此类为与默认系统交互提供可编程接口。默认系统允许程序定制符合用户呈现的的行为。

方法：
    Getting Default Values
    – arrayForKey:
    – boolForKey:
    – dataForKey:
    – dictionaryForKey:
    – floatForKey:
    – integerForKey:
    – objectForKey:
    – stringArrayForKey:
    – stringForKey:
    – doubleForKey:
    – URLForKey:
    Setting Default Values
    – setBool:forKey:
    – setFloat:forKey:
    – setInteger:forKey:
    – setObject:forKey:
    – setDouble:forKey:
    – setURL:forKey:
    Removing Defaults
    – removeObjectForKey:

- synchronize:此函数是自动执行，用于保存此类的修改数据。手工调用此函数，一般情况都是在退出时候需要及时保存，不再等待自动保存。

类方法：
    standardUserDefaults:返回共享默认对象，类型是NSUserDefaults

UIApplicationDelegate Protocol（UIApplicationDelegate协议接口）

The UIApplicationDelegate protocol declares methods that are implemented by the delegate of the singleton UIApplication object.
    UIApplicationDelegate协议接口声明单件UIApplication对象的委托函数方法。

大部分都是采用默认执行，在实际开发中需要的毕竟是少数，此例子用了applicationWillTerminate，就是说程序中断时触发

罗列下：
    Monitoring Application State Changes
    – application:didFinishLaunchingWithOptions:
    – applicationDidBecomeActive:
    – applicationWillResignActive:
    – applicationDidEnterBackground:
    – applicationWillEnterForeground:
    – applicationWillTerminate:
    – applicationDidFinishLaunching:
    Opening a URL Resource
    – application:handleOpenURL:
    – application:openURL:sourceApplication:annotation:
    Managing Status Bar Changes
    – application:willChangeStatusBarOrientation:duration:
    – application:didChangeStatusBarOrientation:
    – application:willChangeStatusBarFrame:
    – application:didChangeStatusBarFrame:
    Responding to System Notifications
    – applicationDidReceiveMemoryWarning:
    – applicationSignificantTimeChange:
    Handling Remote Notifications
    – application:didReceiveRemoteNotification:
    – application:didRegisterForRemoteNotificationsWithDeviceToken:
    – application:didFailToRegisterForRemoteNotificationsWithError:
    Handling Local Notifications
    – application:didReceiveLocalNotification:
    Responding to Content Protection Changes
    – applicationProtectedDataWillBecomeUnavailable:
    – applicationProtectedDataDidBecomeAvailable:

最后说明下，在测试中没有测试出那段代码~~也就是说没有找到触发那个applicationWillTerminate的方法。

PS：再次说明下，+类方法,-成员方法；:意味此方法带有参数