C# 0 The Complete Reference

PART II

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Object

Object

 is the class that underlies the C# 

object

 type. The members of 

Object

 were discussed 

in Chapter 11, but because of its central role in C#, its methods are repeated in Table 21-16 

for your convenience. 

Object

 defines one constructor, which is shown here:

public Object( )

It constructs an empty object.

The IComparable and IComparable Interfaces

Many classes will need to implement either the 

IComparable

 or 

IComparable

 interface 

because it enables one object to be compared to another by various methods defined by the 

.NET Framework. Chapter 18 introduced the 

IComparable

 and 

IComparable

 interfaces, 

where they were used to enable two objects of a generic type parameter to be compared. They 

were also mentioned in the discussion of 

Array

, earlier in this chapter. However, because of 

their importance and applicability to many situations, they are formally examined here.

IComparable

 is especially easy to implement because it consists of just this one method:

int CompareTo(object 

v

)

This method compares the invoking object against the value in 

v.

 It returns greater than zero 

if the invoking object is greater than 

v,

 zero if the two objects are equal, and less than zero if 

the invoking object is less than 

v.

Method

Purpose

public vir tual bool Equals(object 

ob

)

Returns true if the invoking object is the same 

as the one referred to by 

object.

 Returns false 

other wise.

public static bool Equals(object 

ob1

, object 

ob2

)

Returns true if 

ob1

 is the same as 

ob2.

 Returns 

false other wise.

protected Finalize( )

Per forms shutdown actions prior to garbage 

collection. In C#, 

Finalize( ) 

is accessed through 

a destructor.

public vir tual int GetHashCode( )

Returns the hash code associated with the 

invoking object.

public Type GetType( )

Obtains the type of an object at runtime.

protected object Member wiseClone( )

Makes a “shallow copy” of the object. This 

is one in which the members are copied, but 

objects referred to by members are not.

public static bool ReferenceEquals(object 

ob1

,

                                                    object 

ob2

)

Returns true if 

ob1

 and 

ob2

 refer to the same 

object. Returns false other wise.

public vir tual string ToString( )

Returns a string that describes the object.

T

ABLE

 21-16 

Methods Defi ned by 

Object

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The generic version of 

IComparable

 is declared like this:

public interface IComparable

In this version, the type of data being compared is passed as a type argument to 

T

. This 

causes the declaration of 

CompareTo( ) 

to be changed, as shown next.

int CompareTo(T 

obj

)

Here, the type of data that 

CompareTo( ) 

operates on can be explicitly specified. This 

makes

IComparable

 type-safe. For this reason, 

IComparable

 is now preferable 

to