面试之面向对象

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系统学一下OOP英文面试表述

总览

OOPs 的基本概念

  • What is OOPs
    • OOPs refers to Object-Oriented Programming.
    • Class is an abstract/virtual template/blueprint/idea to create instance of objects.
    • Class can contain attributes and methods(functions)
    • Objects are instances of classes created with specific data.
    • Class do NOT use any memory. When create objects needs memory.
  • Why OOPs
    • For big projects, OOPs have lots of advatage than Procedural Programming
    • Thanks to Class, make complex things as reproducible(可重现的), simple structures.
    • Thanks to Inheritance, make code easier to reuse and maintain.
    • Thanks to Encapsulation, make code secure and easier to understand and maintain
    • Thanks to Abstraction, make code simple and secure and easier to maintain
    • Thanks to Polymorphism, make code, easier to reuse and understand
  • Features or Principles
    • Inheritance(继承): child classes inherit data and behaviors from parent class
    • Encapsulation(封装): containing all information in an object, exposing only selected information
    • Abstraction(抽象): only exposing public methods for accessing an object
    • Polymorphism(多态性): many methods can do the same task

更多的细节

  • types of Polymorphism(多态性)
    • Compile Time Polymorphism(编译时多态) / Static Polymorphism(静态多态):
      • the type Polymorphism that happens at compile time
      • So the compiler decides which methods to be called
    • Runtime Polymorphism(运行时多态) / Dynamic Polymorphism(动态多态):
      • the type of Polymorphism that happens at the run time
      • use it when the compiler can NOT choose right methods by parameters.
  • How C++ support Polymorphism
    • For Static Polymorphism: based on templates, function overloading and default arguments
    • For Dynamic Polymorphism: based on virtual functions
  • Is it always necessary to create objects from class?
    • No, if class including static attributes or static methods, can use these attributes and methods directly.
  • What is a constructor (构造函数)?
    • Constructors are special methods whose name is the same as the class name.
    • The purpose is instantiate the class and do some init jobs.
  • various types of constructors in C++
    • Default constructor: constructor without any parameters.
    • Parameterized constructor: constructor’s parameter with some arguments.
    • Copy constructor: constructor’s parameter with onther object of the same class.
  • What is a destructor (解构函数)?
    • destructors free up the resources and memory occupied by an object
    • Destructors are automatically called when an object is being destroyed.
  • Different between class and structure(结构体)
    • class is saved in the heap memory
    • structure is saved in the stack memory
    • structure has NO data abstraction.
  • any limitations of Inheritance?
    • needs more time to process.
    • the base class and the child class, are very tightly coupled (紧密耦合)
    • in some case, Inheritance might be complex for implementation
  • Types of inheritance
    • Single inheritance (单继承, 父类子类两代)
    • Multiple inheritances (多重继承, 1个子类多个父类)
    • Multi-level inheritance (多级继承, 三代)
    • Hierarchical inheritance (分层继承, 1个父类多个子类)
    • Hybrid inheritance (混合继承)
  • Name in inheritance
    • child class, subclass, derived class
    • parent class, superclass, base class
    • interface: special type of class
      • only allowed methods declaration, No definition.
      • can NOT create objects for interface.
      • you need to implement interface and define methods for their implementation
  • Overloading vs Overriding
    • Overloading is a compile-time polymorphism feature.
    • Example: Method overloading and Operator overloading
    • Overriding is a runtime polymorphism feature.
    • Example: Method overriding
  • abstract class(抽象类) vs interface
    • 相同点: 都是特殊的类. 都不能实例化, 都包含抽象的方法.
    • special types of classes. contain only the methods declaration. can NOT be an object directly.
    • 主要区别: 实现接口时, 必须定义和实现所有方法. 继承抽象类时, 子类可以不定义其抽象方法.
    • when an interface is implemented, the subclass must define all its methods and provide its implementation.
    • when an abstract class is inherited, the subclass does not have to provide the definition of its abstract method
  • What are access specifiers(访问说明符)
    • a special type of keywords, inlcude private, public, etc
    • to achieve Encapsulation
  • What is Garbage Collection in OOPs world
    • Each object consumes memory when it created from class.
    • Garbage collection is a mechanism of handling the memory in the program.
    • Garbage collection will free up memory when objects are no longer needed

参考资料

原创于 DRA&PHO