Visual Component Library

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VCL (Visual Component Library) is a visual component-based framework for developing Microsoft Windows applications, developed by Borland for use in its Delphi and C++ Builder software development environment. It is written in Object Pascal.

Much of the popularity of the VCL comes from its tight integration with visual RAD tools from Borland.

A cross-platform equivalent of the VCL called CLX (Component Library for Cross Platform) was later developed for use in Delphi, C++ Builder and Kylix, it was however abandoned in favor of the VCL.

As an object-oriented approach, the VCL forms an object hierarchy where all other objects inherit or indirectly inherit the TObject class (thus, TObject is a superclass). This is a common approach shared by the Java programming language, Smalltalk, and many other object-oriented programming languages.

VCL components cover Windows controls like windows (TForm class), controls (e.g., TButton, TCheckBox, TLabel classes) as well as database access (e.g., ADO or IBX components) or Internet connections (Indy components). The component approach allows programmers to extend the VCL with many visual and non-visual additional components. The best known component packages are JEDI or TMS.

While not all VCL components are thread-safe, VCL supports multi-threading too.

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