Design patterns are reusable solutions to common problems that arise in software design. They are described as patterns because they can be applied in various contexts and provide a common vocabulary for discussing design issues.

There are several types of design patterns in software engineering, including creational, structural, and behavioral patterns. Some common design patterns in Java include:

• Singleton pattern: This creational pattern ensures that a class has only one instance and provides a global point of access to it.
• Factory pattern: This creational pattern provides an interface for creating objects in a super class, but allows subclasses to alter the type of objects that will be created.
• Adapter pattern: This structural pattern allows two incompatible interfaces to work together by wrapping one interface in an adapter class.
• Decorator pattern: This structural pattern allows adding new behavior to an existing object dynamically by wrapping it in a decorator class.
• Observer pattern: This behavioral pattern allows an object to notify other objects about changes in its state, and allows other objects to register and unregister themselves as observers.

Design patterns are not a one-size-fits-all solution, and the choice of which pattern to use depends on the specific problem you are trying to solve. However, understanding and using design patterns can help you write more maintainable, flexible, and reusable code.

For more information on design patterns in Java, you can refer to the “Design Patterns: Elements of Reusable Object-Oriented Software” book by the Gang of Four (Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides), or you can refer to the Java documentation:

• Design Patterns: https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/doc-files/Patterns.html
• Creational patterns: https://docs.oracle.com/en/java/javase/