Different design patterns for the same action within the same app

1. Can a project have multiple design patterns?
2. Can we use each design pattern only once per application?
3. Which one of the design patterns says to reuse already existing similar?
4. Can you combine design patterns?

Can a project have multiple design patterns?

You do not have to use one pattern for every piece of functionality. In fact, many pieces of functionality don't use patterns at all, and some pieces will use multiple patterns.

Can we use each design pattern only once per application?

Design patterns is used to solve specific programming problems. They are not used to architecture your applications. 1) Can I have multiple design patterns in the application? Yes.

Which one of the design patterns says to reuse already existing similar?

Flyweight pattern tries to reuse already existing similar kind objects by storing them and creates new object when no matching object is found.

Can you combine design patterns?

It's perfectly fine to combine design patterns as long as they do not interfere with one another or to eliminate any concerns. Doing so, you gain the benefits of both patterns while removing the need to write extraneous and sparse code that you may have when you create many abstractions.