Programming C# 3.0, 5th Edition

Creating Objects

In Chapter 3, we drew a distinction between value types and reference types. The primitive C# types (int, char, etc.) are value types, and when they are created as standalone variables (not as part of other objects) they are created on the stack. Objects, however, are reference types and are created on the heap, using the keyword new, as in the following:

Time t = new Time(  );

t doesn't actually contain the value for the Time object; it contains the address of that (unnamed) object that is created on the heap. t itself is just a reference to that object.

Tip

VB 6 programmers take note: although there is a performance penalty in using the VB 6 keywords Dim and New on the same line, in C#, this penalty doesn't exist. Thus, in C#, there is no drawback to using the new keyword when declaring an object variable.

Constructors

In Example 4-1, notice that the statement that creates the Time object looks as though it is invoking a method:

Time t = new Time(  );

In fact, a method is invoked whenever you instantiate an object. This method is called a constructor, and you must either define one as part of your class definition or let the compiler 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 undifferentiated memory; after the constructor completes, the memory holds a valid instance of the class type.

The Time class of Example 4-1 doesn't define a constructor. ...