01.里氏准换与using关键字

Posted 2020-08-17

using关键字有什么用？什么是IDisposable？

using可以声明namespace的引入，还可以实现非托管资源的释放，实现了IDisposiable的类在using中创建，using结束后会自动调用该对象的Dispose方法，释放资源。加分的补充回答：using其实等价于try……finally，用起来更方便。

里氏转换

(1).子类可以赋值给父类

(2).如果父类中装的是子类对象,那么可以将这个父类强制转换为子类对象.

得出结论:子类对象可以调用父类的成员,但是父类只能调用自己的成员.

注:子类可以转换成父类有什么意义?

有时候,有的地方需要一个父类对象,这个时候,我们可以使用这个父类的一个子类

来代替.(因为子类可以赋值给父类.)

对于里氏转换的判断

is   表示类型转换,如果能够转换成功,则返回一个true,否则返回一个false

is的使用方法:

if (p1 is Tether)
            {
                Tether t1 = (Tether)p1;
                t1.TetherSayHello();
            }
            else
            {
                Console.WriteLine("转换失败");
            }

as  表示类型转换,如果能够转换转换成功,则返回对应的对象,否则返回一个null.

as的使用方法:

Student s3 = p1 as Student;
            s3.StudentSayHello();

里氏转换的练习01:

namespace _02.里氏装换的练习
{
    class Program
    {
        static void Main(string[] args)
        {
            /*
            自己定义一个父类Person,两个子类Teacher和Student类.
            Person写一个有参数的构造方法.
            */
            /*
            自己试试,子类可以自动转父类,父类转子类要通过强转.
            为了不出错,可以先通过is判断或用as转换.
            */
            Person p1;
            Student s1 = new Student("张三", 18, ‘男‘);
            if (s1 is Person)   //使用is进行转换
            {
                p1 = s1;
                Console.WriteLine("转换成功");
            }
            else
            {
                Console.WriteLine("转换失败");
            }
            Person p2;
            Teacher t1 = new Teacher("小兰", 16, ‘女‘);
            p2 = t1 as Person;   //使用as进行转换
            if (p2 != null)
            {
                Console.WriteLine("转换成功");
            }
            else
            {
                Console.WriteLine("转换失败");
            }
            Console.ReadKey();
            
        }
    }
    public class Person
    {
        public Person(string name, int age, char gender)
        {
            this.Name = name;
            this.Age = age;
            this.Gender = gender;
        }
        private string _name;
        public string Name
        {
            get
            {
                return _name;
            }
            set
            {
                _name = value;
            }
        }  //Name属性定义结束
        public int Age
        {
            get
            {
                return _age;
            }
            set
            {
                _age = value;
            }
        }  //Age属性定义结束
        public char Gender
        {
            get
            {
                return _gender;
            }
            set
            {
                _gender = value;
            }
        } //_gender属性定义结束
        private int _age;
        private char _gender;
        public void PersonSayHello()
        {
            Console.WriteLine("我是父类");
        }
    }  //Person 类定义结束
    public class Student:Person
    {
        public Student(string name, int age, char gender):base(name,age, gender)
        {
        }
        public void StudentSayHello()
        {
            Console.WriteLine("我是学生");
        }  
    }//Student 类定义结束
    public class Teacher : Person
    {
        public Teacher(string name, int age, char gender) : base(name, age, gender)
        {
        }
        public void TeacherSayHello()
        {
            Console.WriteLine("我是老师");
        }
    }
}

 

里氏转换的练习02:

namespace _03.子类赋值给父类的练习01
{
    class Program
    {
        static void Main(string[] args)
        {
            Person[] p1 = new Person[10];
            Random r = new Random();
            int random = 0;   //保存随机数
            for (int i = 0; i < p1.Length; i++)
            {
                random=r.Next(1, 7);   //从1`6随机产生一个数
                switch (random)
                {
                    case 1:
                        p1[i] = new Student();
                        break;
                    case 2:
                        p1[i] = new Teacher();
                        break;
                    case 3:
                        p1[i] = new MeiLv();
                        break;
                    case 4:
                        p1[i] = new YeShou();
                        break;
                    case 5:
                        p1[i] = new ShuaiGuo();
                        break;
                    case 6:
                        p1[i] = new Person ();
                        break;                        
                }
               
                
            }
            for (int i = 0; i < p1.Length; i++)
            {
                if (p1[i] is Student)
                {
                    ((Student)p1[i]).StudentSayHello();
                }
                else if (p1[i] is Teacher)
                {
                    ((Teacher)p1[i]).ThacherSayHello();
                }
                else if (p1[i] is MeiLv)
                {
                    ((MeiLv)p1[i]).MeiLvSayHello();
                }
                else if (p1[i] is Person)
                {
                    p1[i].PersonSayHello();
                }
                else if (p1[i] is YeShou)
                {
                    ((YeShou)p1[i]).YeShouSayHello();
                }
                else if (p1[i] is ShuaiGuo)
                {
                    ((ShuaiGuo)p1[i]).ShuaiGuoSayHello();
                }
            }
            Console.ReadKey();
        }
    }
    public class Person
    {
        public void PersonSayHello()
        {
            Console.WriteLine("我是人类");
        }
    }
    public class Student : Person
    {
        public void StudentSayHello()
        {
            Console.WriteLine("我是学生");
        }
    }
    public class Teacher : Person
    {
        public void ThacherSayHello()
        {
            Console.WriteLine("我是老师");
        }
    }
    public class YeShou : Person
    {
        public void YeShouSayHello()
        {
            Console.WriteLine("我是野兽");
        }
    }
    public class ShuaiGuo:Person
    {
        public void ShuaiGuoSayHello()
        {
            Console.WriteLine("我是帅锅");
        }
    }
    public class MeiLv:Person
    {
        public void MeiLvSayHello()
        {
            Console.WriteLine("我是美女");
        }
    }
  
}

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