System.Object class

  • Article

This article provides supplementary remarks to the reference documentation for this API.

The Object class is the ultimate base class of all .NET classes; it is the root of the type hierarchy.

Because all classes in .NET are derived from Object, every method defined in the Object class is available in all objects in the system. Derived classes can and do override some of these methods, including:

  • Equals: Supports comparisons between objects.
  • Finalize: Performs cleanup operations before an object is automatically reclaimed.
  • GetHashCode: Generates a number corresponding to the value of the object to support the use of a hash table.
  • ToString: Manufactures a human-readable text string that describes an instance of the class.

Languages typically don't require a class to declare inheritance from Object because the inheritance is implicit.

Performance considerations

If you're designing a class, such as a collection, that must handle any type of object, you can create class members that accept instances of the Object class. However, the process of boxing and unboxing a type carries a performance cost. If you know your new class will frequently handle certain value types you can use one of two tactics to minimize the cost of boxing.

  • Create a general method that accepts an Object type, and a set of type-specific method overloads that accept each value type you expect your class to frequently handle. If a type-specific method exists that accepts the calling parameter type, no boxing occurs and the type-specific method is invoked. If there is no method argument that matches the calling parameter type, the parameter is boxed and the general method is invoked.
  • Design your type and its members to use generics. The common language runtime creates a closed generic type when you create an instance of your class and specify a generic type argument. The generic method is type-specific and can be invoked without boxing the calling parameter.

Although it's sometimes necessary to develop general purpose classes that accept and return Object types, you can improve performance by also providing a type-specific class to handle a frequently used type. For example, providing a class that is specific to setting and getting Boolean values eliminates the cost of boxing and unboxing Boolean values.