Learn how Java systems combine patterns around one design problem and how to keep those combinations coherent instead of architecturally noisy.
Real Java systems rarely solve a serious design problem with exactly one pattern. More often, a feature or subsystem uses several smaller pattern choices that reinforce each other.
A service endpoint might combine:
The danger is not that patterns combine. The danger is combining them without a clear ownership model.
When multiple patterns appear in one area, ask which pressure is primary:
The primary pressure should drive the structure. The other patterns should support it, not compete with it.
Pattern combinations are good when they make the subsystem easier to:
If the combination makes the code harder to narrate, you probably have too many abstractions for the actual problem.