20250530-C#知识：万物之父Object

news2025/7/23 19:01:39

C#知识：万物之父Object

Object类（即object）是所有类的基类，这里面的方法还是需要好好了解一下。

1、Object类

是顶级父类，其他类默认都是Object类的子类（自定义类也会默认继承Object类）
可以用Object变量装载值类型和其他自定义类型对象
Object类是引用类型
存在装箱拆箱

object x = 100; //装箱
int y = (int)x; //拆箱

2、Object类中的静态方法

2.1 静态方法Equals

判断两个参数是否相等
调用第一个参数的虚拟Equals方法进行判断，无论值类型和引用类型

public static bool Equals(object? objA, object? objB);

2.2 静态方法ReferenceEquals

比较两个引用类型对象是否相等
传递值类型则返回false

public static bool ReferenceEquals(object? objA, object? objB);

3、Object类的成员方法

3.1 普通方法GetType

返回对象类型的Type对象，可用于反射

public extern Type GetType();

3.2 普通方法MemberwiseClone

获取对象的浅拷贝对象
对象的引用类型成员变量也是直接拷贝，指向堆中相同位置

protected unsafe object MemberwiseClone();

4、Object类的虚拟方法

4.1 虚拟方法Equals

只有一个参数，将调用方法的对象与参数对象进行比较
引用类型比较引用（默认）
值类型比较值是否相等，因为System.ValueType中重写了该方法
测试了枚举和结构体，也符合值类型的比较规则

public virtual bool Equals(object? obj)

4.2 虚拟方法GetHashCode

获取对象哈希值

public virtual int GetHashCode()

4.3 虚拟方法ToString

将对象进行打印输出时默认调用此方法

public virtual string? ToString()

5、完整测试用例：

namespace LearnObject
{
    enum Daily
    {
        Eat,
        Sleep
    }
    struct Point
    {
        public int x;
        public int y;

        public Point():this(0,0) { }
        public Point(int x, int y)
        {
            this.x = x;
            this.y = y;
        }
    }
    class Student
    {
        public string name;
        public int age;
        public Teacher teacher;


        public Student():this("张飞",18, new Teacher()) { }

        public Student(string name, int age)
        {
            this.name = name;
            this.age = age;
            this.teacher = new Teacher();
        }
        public Student(string name, int age, Teacher teacher) : this(name, age)
        {
            this.teacher = teacher;
        }

        public override bool Equals(Object? a)
        {
            if (a != null && a is Student)
            {
                Student other = a as Student;
                return this.name.Equals(other.name) && this.age == other.age;
            }
            return false;
        }

        public override int GetHashCode()
        {
            Console.WriteLine($"重写之前的哈希值： {base.GetHashCode()}");
            return 10086;   //自定义哈希逻辑
        }

        public override string ToString()
        {
            return $"自定义输出，学生的名字：{this.name}，年龄：{this.age} \n" ;
        }

        public Student ShallowClone() => this.MemberwiseClone() as Student;
    }

    class Student2
    {
        public string name;
        public int age;
        public Teacher teacher;

        public Student2() : this("张飞", 18, new Teacher()) { }

        public Student2(string name, int age)
        {
            this.name = name;
            this.age = age;
            this.teacher = new Teacher();
        }

        public Student2(string name, int age, Teacher teacher) : this(name, age)
        {
            this.teacher = teacher;
        }

        public Student2 ShallowClone() => this.MemberwiseClone() as Student2;
    }

    class Teacher
    {
        public string name;

        public Teacher() { this.name = "诸葛亮"; }

        public Teacher(string name)
        {
            this.name = name;
        }   
    }
    internal class Program
    {
        static void Main(string[] args)
        {

            object x = 100; //装箱
            int y = (int)x; //拆箱
            
            Student student1 = new Student();
            Student student2 = new Student();
            Student2 student3 = new Student2();
            Student2 student4 = new Student2();
            Console.WriteLine(Equals(student1, student2));  //True  //因为Student中Equals方法被重写了
            Console.WriteLine(Equals(student3, student4));  //False //因为Student2默认比较的是引用

            Console.WriteLine(ReferenceEquals(student1, student2)); //False
            Console.WriteLine(ReferenceEquals(5, 5));
            Point point1 = new Point(1, 1); //测试结构体
            Point point2 = new Point(1, 1);
            Daily daily1 = Daily.Sleep; //测试枚举
            Daily daily2 = Daily.Sleep;
            Console.WriteLine(ReferenceEquals(point1, point2)); //False
            Console.WriteLine(Equals(point1, point2));  //True
            Console.WriteLine(ReferenceEquals(daily1, daily2)); //False
            Console.WriteLine(Equals(daily1, daily2));  //True

            Type type = student1.GetType();
            Console.WriteLine(type.ToString()); //LearnObject.Student

            Student student5 = new Student("关羽",20, new Teacher("诸葛亮"));
            Student student6 = student5.ShallowClone();
            Console.WriteLine("修改前");
            Console.WriteLine($"学生5：{student5.name}的老师是{student5.teacher.name}");   //学生5：关羽的老师是诸葛亮
            Console.WriteLine($"学生6：{student6.name}的老师是{student6.teacher.name}");   //学生6：关羽的老师是诸葛亮

            student6.name = "刘备";
            student5.teacher.name = "庞士元";
            Console.WriteLine("学生6修改后");
            Console.WriteLine($"学生5：{student5.name}的老师是{student5.teacher.name}");   //学生5：关羽的老师是庞士元
            Console.WriteLine($"学生6：{student6.name}的老师是{student6.teacher.name}");   //学生6：刘备的老师是庞士元

            Student student7 = new Student();
            Student2 student8 = new Student2();
            Console.WriteLine(student7.GetHashCode());  //10086 
            Console.WriteLine(student8.GetHashCode());  //18643596
            Console.WriteLine(student7.ToString()); //自定义输出，学生的名字：张飞，年龄：18
            Console.WriteLine(student8.ToString()); //LearnObject.Student2
        }
    }
}