摘要：object composition (Decorator pattern) is often a better technique than subclassing for extending class behavior.1.Abstract Factoryprovides an interface for creating families of related or dependent objects without specifying their concrete classes提供接口创建相同或类似的对象，不需要指定其具体的类型iso中主要体现在NSNumber和NSArray和 阅读全文

摘要：When a low-memory condition occurs, the system may purge suspended apps without notice to make more space for the foreground app.The main difference is that instead of your app being made active, it enters the background state to handle the event and then is suspended shortly afterward. When launchi 阅读全文

摘要：/*!* @class Calculator* This class implements a key-press--based calculator engine.* @throws NSInvalidArgumentException*/#import <Foundation/Foundation.h>@interface Calculator : NSObject {@private NSMutableString *_display; // The calculator display (the value a harwdare-based calculator shows 阅读全文