Can you explain the differences between the Decorator and Adapter patterns in software design?

The Decorator and Adapter patterns solve different problems, although both work with objects and can use composition.

Decorator is a structural pattern that allows dynamically adding new responsibilities to objects by wrapping them in other decorator objects. It preserves the interface of the original object, extending its behavior without changing the code.

Adapter is a pattern that allows objects with incompatible interfaces to work together. It transforms the interface of one class into the interface expected by the client.

Example:

• Decorator: there is an object Window, and we want to add a border to it without changing the original class. We create BorderDecorator, which wraps Window and adds a border.
• Adapter: there is a class OldPrinter with a method printOld(), and the client expects a method print(). We create PrinterAdapter, which implements the print() method and internally calls printOld().

Thus:

• The Decorator extends the behavior of the object.
• The Adapter changes the object's interface for compatibility.