Explain Decorator Design Pattern in Java

Decorator design pattern attaches additional responsibilities or functions, dynamically or statically on an object.One can add new functionalities on an object without affecting other objects enhancing flexibility of an object.

The best example of Decorator pattern in a visual manner can be illustrated from JScrollPane object which can be used to decorate a JTextArea object or a JEditorPane object. The different borders of a window like BevelBorder, CompoundBorder, EtchedBorder TitledBorder etc. are other examples of classes working as decorators existent in Java API.

Decorator pattern can be used in a non-visual fashion. For example, BufferedInputStream, DataInputStream, and CheckedInputStream are decorating objects of FilterInputStream class. These decorators are standard Java API classes.