Talk about classes and objects in Delphi: Iv. abstract classes and their examples

Iv. abstract classes and instances of it

Delphi has a class called abstract class, you can not naïve directly create an instance for it, such as

var    strlst:tstring;begin    strlst:= tstring.create;    Strlst.add (' I love China ');    Strlst.free;end;

This is wrong, because Tstring is an abstract class.

So how do you construct an instance for such an abstract class? The answer is to use its non-abstract subclasses. We know that Tstring has a non-abstract subclass of Tstringlist. So you can do this.

var    strlst:tstring;    Or can be declared through the abstract class    //or directly with Strlst:tstringlist;    But the former better some begin    strlst:= tstringlist.create;    However, creating a concrete object must use a non-abstract subclass of the abstract class         //And the created instance is in memory the structure of its subclass,         //Although the abstract class declaration is used in Var, but the specific create is its non-abstract subclass    Strlst.add (' I love China ');    Strlst.free;end;

　　

　　

Talk about classes and objects in Delphi: Iv. abstract classes and their examples