{"id":425,"date":"2022-01-07T17:33:34","date_gmt":"2022-01-07T10:33:34","guid":{"rendered":"https:\/\/csharptutorial.net\/?page_id=425"},"modified":"2022-06-03T15:04:22","modified_gmt":"2022-06-03T08:04:22","slug":"csharp-object","status":"publish","type":"page","link":"https:\/\/www.csharptutorial.net\/csharp-tutorial\/csharp-object\/","title":{"rendered":"C# object"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn about the C# Object class and how to override the methods of the Object<\/code> class including ToString()<\/code>, Equals()<\/code>, and GetHashCode()<\/code>.<\/p>\n\n\n\n

Introduction to the C# object class<\/h2>\n\n\n\n

All types in .NET implicitly inherit from the System.Object<\/code> class. In other words, the System.Object<\/code> is the base class of all classes. The System.Object<\/code> class provides low-level functionalities to the subclasses.<\/p>\n\n\n\n

Note that the object is a synonym for the System.Object<\/code> class. Therefore, they refer to the same object.<\/p>\n\n\n\n

When you define a class<\/a>, it is implicitly inherited from the System.Object<\/code> class. And you don’t need to explicitly specify it. <\/p>\n\n\n\n

The following example defines the Person<\/code> class:<\/p>\n\n\n

class<\/span> Person<\/span>\n{\n    public<\/span> string<\/span> SSN { get<\/span>; set<\/span>; }\n    public<\/span> string<\/span> Name { get<\/span>; set<\/span>; }\n    public<\/span> byte<\/span> Age { get<\/span>; set<\/span>; }\n\n    public<\/span> Person<\/span>(string<\/span> ssn, string<\/span> name, byte<\/span> age<\/span>)<\/span>\n    {\n        SSN = ssn;\n        Name = name;\n        Age = age;\n    }\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
In this example, the Person<\/code> class implicitly inherits from the System.Object<\/code> class. It can reuse or customize the methods in the Object<\/code> class.<\/p>\n\n\n\n
For example, the GetType()<\/code> method returns the type of an instance of a class:<\/p>\n\n\n
\/\/ Program.cs<\/span>\n\nvar<\/span> p1 = new<\/span> Person(\"545\u201357-1111\"<\/span>, \"John Doe\"<\/span>, 25<\/span>);\nConsole.WriteLine(p1.GetType());<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
Person<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
In this example, we call the GetType()<\/code> method on an instance of the Person<\/code> class. Therefore, its type is Person<\/code>.<\/p>\n\n\n\n
ToString()<\/h2>\n\n\n\n
The ToString()<\/code> method returns the string representation of an object. By default, the ToString()<\/code> returns the type of the object. For example:<\/p>\n\n\n
\/\/ Program.cs<\/span>\n\nvar<\/span> p1 = new<\/span> Person(\"545\u201357-1111\"<\/span>, \"John Doe\"<\/span>, 25<\/span>);\nConsole.WriteLine(p1.ToString());<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
Person<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Note that you don’t need to call the ToString()<\/code> method explicitly:<\/p>\n\n\n
\/\/ Program.cs<\/span>\n\nvar<\/span> p1 = new<\/span> Person(\"545\u201357-1111\"<\/span>, \"John Doe\"<\/span>, 25<\/span>);\nConsole.WriteLine(p1);<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
To customize the string representation of an object, you can override the ToString()<\/code> method of the System.Object<\/code> the class. For example:<\/p>\n\n\n
class<\/span> Person<\/span>\n{\n    public<\/span> string<\/span> SSN { get<\/span>; set<\/span>; }\n    public<\/span> string<\/span> Name { get<\/span>; set<\/span>; }\n    public<\/span> byte<\/span> Age { get<\/span>; set<\/span>; }\n\n    public<\/span> Person<\/span>(string<\/span> ssn, string<\/span> name, byte<\/span> age<\/span>)<\/span>\n    {\n        SSN = ssn;\n        Name = name;\n        Age = age;\n    }\n\n    public<\/span> override<\/span> string<\/span> ToString<\/span>(<\/span>)<\/span>\n    {\n        return<\/span> $\"Person(ssn={SSN}<\/span>,name={Name}<\/span>,age={Age}<\/span>)\"<\/span>;\n\n    }\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
In this example, we override the ToString()<\/code> method of the System.Object<\/code> class to return a string representation of the Person<\/code>‘s objects.<\/p>\n\n\n
\/\/ Program.cs<\/span>\n\nvar<\/span> p1 = new<\/span> Person(\"545\u201357-1111\"<\/span>, \"John Doe\"<\/span>, 25<\/span>);\nConsole.WriteLine(p1);<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
Person(ssn=545<\/span>-57<\/span>-1111<\/span>,name=John Doe,age=25<\/span>)<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Equals()<\/h2>\n\n\n\n
To compare two objects, you use the Equals<\/code> method of the System.Object<\/code> class. <\/p>\n\n\n\n
Typically, you need to override the Equals<\/code> method in your class to specify the logic to determine if two objects are equal. For example:<\/p>\n\n\n
class<\/span> Person<\/span>\n{\n    public<\/span> string<\/span> SSN { get<\/span>; set<\/span>; }\n    public<\/span> string<\/span> Name { get<\/span>; set<\/span>; }\n    public<\/span> byte<\/span> Age { get<\/span>; set<\/span>; }\n\n    public<\/span> Person<\/span>(string<\/span> ssn, string<\/span> name, byte<\/span> age<\/span>)<\/span>\n    {\n        SSN = ssn;\n        Name = name;\n        Age = age;\n    }\n\n    public<\/span> override<\/span> string<\/span> ToString<\/span>(<\/span>)<\/span>\n    {\n        return<\/span> $\"Person(ssn={SSN}<\/span>,name={Name}<\/span>,age={Age}<\/span>)\"<\/span>;\n\n    }\n\n    public<\/span> override<\/span> bool<\/span> Equals<\/span>(object<\/span>? obj<\/span>)<\/span>\n    {\n        if<\/span> (obj == null<\/span> || !GetType().Equals(obj.GetType()))\n        {\n            return<\/span> false<\/span>;\n        }\n\n        var<\/span> other = (Person)obj;\n\n        return<\/span> SSN == other.SSN;\n    }\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
In this example, we override the Equals<\/code> method of the System.Object<\/code> class in the Person<\/code> class. <\/p>\n\n\n\n
If the object is null<\/code> or its type is not the same, the Equals<\/code> method returns false<\/code>. Otherwise, it returns true<\/code> if the social security number (SSN) of two people are the same.<\/p>\n\n\n
\/\/ Program.cs<\/span>\n\nvar<\/span> p1 = new<\/span> Person(\"545\u201357-1111\"<\/span>, \"Jane Doe\"<\/span>, 22<\/span>);\nvar<\/span> p2 = new<\/span> Person(\"545\u201357-1111\"<\/span>, \"Jane Smith\"<\/span>, 23<\/span>);\n\nConsole.WriteLine(p1.Equals(p2));<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
True<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
GetHashCode()<\/h2>\n\n\n\n
The GetHashCode()<\/code> method returns a hash code for the current object. C# uses the hash code returned by the \u00a0GetHashCode()<\/code>\u00a0method to check the object equality.<\/p>\n\n\n\n
If two objects are equal, the GetHashCode()<\/code> method returns the same hash code. However, the reverse is not true. The equal hash codes do not mean object equality because unequal objects can have the same hash codes.<\/p>\n\n\n\n
The following shows how to override the GetHashCode()<\/code> method:<\/p>\n\n\n
class<\/span> Person<\/span>\n{\n    public<\/span> string<\/span> SSN { get<\/span>; set<\/span>; }\n    public<\/span> string<\/span> Name { get<\/span>; set<\/span>; }\n    public<\/span> byte<\/span> Age { get<\/span>; set<\/span>; }\n\n    public<\/span> Person<\/span>(string<\/span> ssn, string<\/span> name, byte<\/span> age<\/span>)<\/span>\n    {\n        SSN = ssn;\n        Name = name;\n        Age = age;\n    }\n\n    public<\/span> override<\/span> string<\/span> ToString<\/span>(<\/span>)<\/span>\n    {\n        return<\/span> $\"Person(ssn={SSN}<\/span>,name={Name}<\/span>,age={Age}<\/span>)\"<\/span>;\n\n    }\n\n    public<\/span> override<\/span> bool<\/span> Equals<\/span>(object<\/span>? obj<\/span>)<\/span>\n    {\n        if<\/span> (obj == null<\/span> || !GetType().Equals(obj.GetType()))\n        {\n            return<\/span> false<\/span>;\n        }\n\n        var<\/span> other = (Person)obj;\n\n        return<\/span> SSN.Equals(other.SSN);\n    }\n\n    public<\/span> override<\/span> int<\/span> GetHashCode<\/span>(<\/span>)<\/span>\n    {\n        return<\/span> SSN.GetHashCode();\n    }\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
Summary<\/h2>\n\n\n\n
  • The System.Object<\/code> is the base class of all classes in .NET<\/li>
  • The object<\/code> is the alias of the System.Object<\/code> class.<\/li>
  • Override the ToString()<\/code> to customize the string representation of the object.<\/li>
  • Override the Equals()<\/code> method to determine if two objects are equal.<\/li>
  • Override the GetHashCode()<\/code> method to return a hash code for the object<\/li><\/ul>\n
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