What is finalize() and Is It Reliable?

Direct Answer

Object.finalize() was a finalization hook that the JVM might invoke after an object became unreachable. Its execution and timing were never guaranteed. The method was deprecated in Java 9 and finalization was deprecated for removal in Java 18; saying it was removed in Java 18 is incorrect. Use AutoCloseable with try-with-resources for deterministic cleanup.

Code Example

import java.io.IOException;
import java.net.Socket;

final class ManagedConnection implements AutoCloseable {
    private final Socket socket;

    ManagedConnection(Socket socket) {
        this.socket = socket;
    }

    @Override
    public void close() throws IOException {
        socket.close();
    }
}

class CleanupExample {
    static void send(Socket socket) throws IOException {
        try (var connection = new ManagedConnection(socket)) {
            // use connection
        } // close() runs on normal or exceptional exit from the try body
    }
}

The owner closes the resource at a known boundary. A finalizer cannot provide that timing guarantee.

Common Mistakes & Pitfalls

• Treating finalize like a deterministic destructor: finalization may happen late or never happen before process exit.
• Using it for resources: a file or connection can remain open while the application waits for an unpredictable GC decision.
• Saying Java 18 removed it: Java 18 deprecated finalization for removal; that is different from immediate removal.
• Replacing explicit ownership with Cleaner: Cleaner can be a last-resort safety net for some native resources, but normal cleanup should still be explicit.