C#知識：萬物之父Object

Object類（即object）是所有類的基類，這里面的方法還是需要好好了解一下。

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1、Object類

• 是頂級父類，其他類默認都是Object類的子類（自定義類也會默認繼承Object類）
• 可以用Object變量裝載值類型和其他自定義類型對象
• Object類是引用類型
• 存在裝箱拆箱
  

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

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2、Object類中的靜態方法

2.1 靜態方法Equals

• 判斷兩個參數是否相等
• 調用第一個參數的虛擬Equals方法進行判斷，無論值類型和引用類型

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

2.2 靜態方法ReferenceEquals

• 比較兩個引用類型對象是否相等
• 傳遞值類型則返回false

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

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3、Object類的成員方法

3.1 普通方法GetType

• 返回對象類型的Type對象，可用于反射

public extern Type GetType();

3.2 普通方法MemberwiseClone

• 獲取對象的淺拷貝對象
• 對象的引用類型成員變量也是直接拷貝，指向堆中相同位置

protected unsafe object MemberwiseClone();

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4、Object類的虛擬方法

4.1 虛擬方法Equals

• 只有一個參數，將調用方法的對象與參數對象進行比較
• 引用類型比較引用（默認）
• 值類型比較值是否相等，因為System.ValueType中重寫了該方法
• 測試了枚舉和結構體，也符合值類型的比較規則

public virtual bool Equals(object? obj)

4.2 虛擬方法GetHashCode

• 獲取對象哈希值

public virtual int GetHashCode()

4.3 虛擬方法ToString

• 將對象進行打印輸出時默認調用此方法

public virtual string? ToString()

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5、完整測試用例：

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("張飛",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($"重寫之前的哈希值： {base.GetHashCode()}");return 10086;   //自定義哈希邏輯}public override string ToString(){return $"自定義輸出，學生的名字：{this.name}，年齡：{this.age} \n" ;}public Student ShallowClone() => this.MemberwiseClone() as Student;}class Student2{public string name;public int age;public Teacher teacher;public Student2() : this("張飛", 18, new Teacher()) { }public Student2(string name, int age){this.name = name;this.age = age;this.teacher = new Teacher();}public Student2(string name, int age, Teacher teacher) : this(name, age){this.teacher = teacher;}public Student2 ShallowClone() => this.MemberwiseClone() as Student2;}class Teacher{public string name;public Teacher() { this.name = "諸葛亮"; }public Teacher(string name){this.name = name;}   }internal class Program{static void Main(string[] args){object x = 100; //裝箱int y = (int)x; //拆箱Student student1 = new Student();Student student2 = new Student();Student2 student3 = new Student2();Student2 student4 = new Student2();Console.WriteLine(Equals(student1, student2));  //True  //因為Student中Equals方法被重寫了Console.WriteLine(Equals(student3, student4));  //False //因為Student2默認比較的是引用Console.WriteLine(ReferenceEquals(student1, student2)); //FalseConsole.WriteLine(ReferenceEquals(5, 5));Point point1 = new Point(1, 1); //測試結構體Point point2 = new Point(1, 1);Daily daily1 = Daily.Sleep; //測試枚舉Daily daily2 = Daily.Sleep;Console.WriteLine(ReferenceEquals(point1, point2)); //FalseConsole.WriteLine(Equals(point1, point2));  //TrueConsole.WriteLine(ReferenceEquals(daily1, daily2)); //FalseConsole.WriteLine(Equals(daily1, daily2));  //TrueType type = student1.GetType();Console.WriteLine(type.ToString()); //LearnObject.StudentStudent student5 = new Student("關羽",20, new Teacher("諸葛亮"));Student student6 = student5.ShallowClone();Console.WriteLine("修改前");Console.WriteLine($"學生5：{student5.name}的老師是{student5.teacher.name}");   //學生5：關羽的老師是諸葛亮Console.WriteLine($"學生6：{student6.name}的老師是{student6.teacher.name}");   //學生6：關羽的老師是諸葛亮student6.name = "劉備";student5.teacher.name = "龐士元";Console.WriteLine("學生6修改后");Console.WriteLine($"學生5：{student5.name}的老師是{student5.teacher.name}");   //學生5：關羽的老師是龐士元Console.WriteLine($"學生6：{student6.name}的老師是{student6.teacher.name}");   //學生6：劉備的老師是龐士元Student student7 = new Student();Student2 student8 = new Student2();Console.WriteLine(student7.GetHashCode());  //10086 Console.WriteLine(student8.GetHashCode());  //18643596Console.WriteLine(student7.ToString()); //自定義輸出，學生的名字：張飛，年齡：18Console.WriteLine(student8.ToString()); //LearnObject.Student2}}
}

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6、參考資料：

1. 《唐老獅C#》

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