Programming Visual Basic 2005

Constructors

In that example, you will create a new instance of the Time class.

 Dim timeObject As New Time();

The parentheses look a lot like a method call. In fact, a method is invoked whenever you instantiate an object. This method is called a constructor. If you don't define one as part of your class definition, the compiler will provide one on your behalf.

The job of a constructor is to create the object specified by a class and to put it into a valid state. Before the constructor runs, the object is just a blob of memory; after the constructor completes, the memory holds a valid instance of the class.

Tip

Any constructor that takes no arguments is called a default constructor. It turns out that the constructor provided by the compiler takes no arguments, and, hence, is a default constructor. This terminology has caused a great deal of confusion. You can create your own default constructor, and if you do not create a constructor at all, the compiler will create a default constructor for you, by default.

If you do not explicilty initialize your member variables, they are initialized to their default values based on their type (integers to 0, strings to the empty string, etc.). Table 18-2 lists the default values assigned to various types.

Table 18-2. Types and their default values

Type	Default value
Numeric (Integer, Long, etc.)	0
Boolean	False
Char	The Unicode character whose code point is 0
Enum	0
Reference	Nothing

Typically, you'll want to define your ...