Identity, aliasing, and escape discipline

Intermediate covered equals/hashCode. The Advanced discipline is aliasing control — knowing exactly how many references point at a mutable object and making illegal aliasing impossible to express:

• Identity vs equality, deliberately: == asks "same object?", equals asks "same value?". Collections, caches, and locks all have opinions about which one they use — IdentityHashMap exists precisely because sometimes identity is the semantics.
• Defensive copies at the boundary: a constructor taking a mutable collection should copy it (List.copyOf(in)); an accessor exposing internal state should hand out an unmodifiable view or a copy. Intermediate taught the what; here the rule is every boundary, every time.
• Immutability as the default answer: an immutable type cannot have aliasing bugs, is safe to share across threads without synchronization, and makes honest cache keys. Prefer records + List.copyOf + final fields.
• Escape analysis starts in your head: returning this from a constructor, registering this with a listener before construction finishes, or storing an internal array in a public field — each is an object escaping before it is safe.

The operational payoff: objects that never mutate after construction need no defensive synchronization anywhere in the program.