A design pattern is an industry standard approach which provides an architectural solution to a common software problem. It is very popular among software developers.

1. It saves time by using the design pattern. There are many java design patterns that we can use in our java based projects.
2. Design Pattern implements the concept of reusability that leads to more robust and highly maintainable code. It helps in reducing total cost of ownership (TCO) of the software product.
3. Design Pattern makes our code easy to understand and debug. It leads to faster development and new members of team understand it easily.

Java Design Patterns are categorized into three types like Creational Design Patterns, Structural Design Patterns, and Behavioral Design Patterns. The detail classifications which are as follows:

Creational Design Patterns

1. Singleton Pattern
2. Factory Pattern
3. Abstract Factory Pattern
4. Builder Pattern
5. Prototype Pattern

Structural Design Patterns

1. Adapter Pattern
2. Composite Pattern
3. Proxy Pattern
4. Flyweight Pattern
5. Facade Pattern
6. Bridge Pattern
7. Decorator Pattern

Behavioral Design Patterns

1. Template Method Pattern
2. Mediator Pattern
3. Chain of Responsibility Pattern
4. Observer Pattern
5. Strategy Pattern
6. Command Pattern
7. State Pattern
8. Visitor Pattern
9. Interpreter Pattern
10. Iterator Pattern
11. Memento Pattern