Important Design Patterns in Java

I found this list of design patterns in Java

1. Creational Patterns : Concerned with creation of Objects. Prototype, Singleton, Builder etc.

2. Structural Patterns : Concerned with structure of Objects and the relationships between them. Decorator, Facade, Adapter etc.

3. Behavioural Patterns : Concerned with interaction between objects. Strategy, Template Method etc.

What are the most important ones that a Java developer may come across ?