Class object

2017-11-03 09:05:04

As we discussed earlier in this chapter, all classes inherit directly or indirectly from the object class (System.Object in the FCL), so its seven methods are inherited by all other classes. Figure 10.19 summarizes object's methods.

Figure 10.19. `object` methods that are inherited directly or indirectly by all classes.

(This item is displayed on pages 501 - 502 in the print version)
Method	Description
`Equals`	This method compares two objects for equality and returns `true` if they are equal and `false` otherwise. The method takes any object as an argument. When objects of a particular class must be compared for equality, the class should override method `Equals` to compare the contents of the two objects. The method's implementation should meet the following requirements:
	It should return `false` if the argument is `null`. It should return `true` if an object is compared to itself, as in `object1.Equals( object1 )`. It should return `true` only if both `object1.Equals( object2 )` and `object2.Equals( object1 )` would return `true`. For three objects, if `object1.Equals( object2 )` returns `true` and `object2.Equals( object3 )` returns `TRue`, then `object1.Equals( object3 )` should also return `true`. A class that overrides the method `Equals` should also override the method `GetHashCode` to ensure that equal objects have identical hashcodes. The default `Equals` implementation determines only whether two references refer to the same object in memory.
`Finalize`	This method cannot be explicitly declared or called. When a class contains a destructor, the compiler implicitly renames it to override the `protected` method `Finalize`, which is called only by the garbage collector before it reclaims an object's memory. The garbage collector is not guaranteed to reclaim an object, thus it is not guaranteed that an object's `Finalize` method will execute. When a derived class's `Finalize` method executes, it performs its task, then invokes the base class's `Finalize` method. `Finalize`'s default implementation is a placeholder that simply invokes the base class's `Finalize` method.
`GetHashCode`	A hashtable is a data structure that relates one object, called the key, to another object, called the value. We discuss `Hashtable` in Chapter 27, Collections. When initially inserting a value into a hashtable, the key's `GetHashCode` method is called. The hashcode value returned is used by the hashtable to determine the location at which to insert the corresponding value. The key's hashcode is also used by the hashtable to locate the key's corresponding value.
`GetType`	Every object knows its own type at execution time. Method `GetType` (used in Section 11.5) returns an object of class `Type` (namespace `System`) that contains information about the object's type, such as its class name (obtained from `Type` property `FullName`).
`MemberwiseClone`	This `protected` method, which takes no arguments and returns an `object` reference, makes a copy of the object on which it is called. The implementation of this method performs a shallow copyinstance variable values in one object are copied into another object of the same type. For reference types, only the references are copied.
`ReferenceEquals`	This `static` method takes two `object` arguments and returns `TRue` if two objects are the same instance or if they are `null` references. Otherwise, it returns `false`.
`ToString`	This method (introduced in Section 7.4) returns a `string` representation of an object. The default implementation of this method returns the namespace followed by a dot and the class name of the object's class.

We discuss several of object's methods throughout this book (as indicated in the table). You can learn more about object's methods in object's online documentation in the Framework Class Library Reference at:

msdn2.microsoft.com/en-us/library/system.object_members

All array types implicitly inherit from class Array in the System namespace, which in turn extends class object. As a result, like all other objects, an array inherits the members of class object. For more information about the class Array, please see Array's documentation in the FCL Reference, at:

msdn2.microsoft.com/en-us/library/system.array_members

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