Why is finalize() deprecated, and what should you use instead?

Object.finalize() was Java's original mechanism for letting an object run cleanup code before the GC reclaims it — but it has enough serious problems that it's been deprecated since Java 9 and is planned for eventual removal:

• No timing guarantee: there's no promise about when finalize() runs relative to an object becoming unreachable — it could be immediately, much later, or (if the JVM exits first) never at all.
• Delays reclamation: an object with a finalize() method requires an extra GC cycle to actually be collected (it must first be queued for finalization, then finalized, then becomes eligible for real collection on a subsequent pass) — this can meaningfully increase memory pressure for objects that override it.
• Can "resurrect" objects: a poorly written finalize() could store this somewhere else, making the "dying" object reachable again — a confusing, hard-to-reason-about possibility.
• Silently swallowed exceptions: an exception thrown from finalize() is caught internally and ignored, so cleanup failures are invisible.
• No ordering guarantee between multiple objects' finalizers, even ones that reference each other.

Modern replacements:

1. try-with-resources (AutoCloseable) — for deterministic, immediate cleanup tied to a clear scope; this should be the default choice whenever cleanup timing matters (closing files, sockets, database connections).

try (var conn = openConnection()) {
    // use conn
} // conn.close() guaranteed here, deterministically

1. java.lang.ref.Cleaner (Java 9+) — for the rarer case where you genuinely need GC-triggered cleanup as a last-resort safety net (e.g., releasing off-heap/native memory if a caller forgot to explicitly close a resource). It registers a cleanup action tied to an object's reachability via a PhantomReference-based mechanism, without any of finalize()'s reliability and exception-swallowing problems.

Rule of thumb: design APIs so callers explicitly close resources (AutoCloseable); reserve Cleaner purely as a defensive backstop, never as the primary cleanup mechanism.