Java Finalize Method (Deprecated)

Object has a method called finalize() that the garbage collector was supposed to call just before destroying an object, so the object could release files, sockets or other resources. It sounded useful, and old code and interview questions still mention it. In practice it was unreliable, slow and dangerous, so it was deprecated in Java 9 and is now marked for removal. This lesson explains why, and shows what to use instead.

The Warning You'll See

public class Fin {
    @Override
    protected void finalize() { System.out.println("cleanup"); }
}

Fin.java:3: warning: [removal] finalize() in Object has been deprecated and marked for removal
    protected void finalize() { System.out.println("cleanup"); }
                   ^
1 warning

It still compiles, but the compiler is telling you that a future Java version will remove it. Since Java 18 you can even switch finalization off completely with java --finalization=disabled, to test whether your program secretly depends on it.

Why It Never Worked Well

What to Use Instead

The right tool is to close resources yourself, at a known moment. Any class can opt in by implementing AutoCloseable, and a try-with-resources statement closes it automatically, even if an exception is thrown:

public class Receipts {
    static class ReceiptPrinter implements AutoCloseable {
        private final String counter;
 
        ReceiptPrinter(String counter) {
            this.counter = counter;
            System.out.println("Printer opened at " + counter);
        }
 
        void print(String customer, long amount) {
            System.out.println("Receipt: " + customer + ", Rs. " + amount);
        }
 
        @Override
        public void close() {
            System.out.println("Printer closed at " + counter);
        }
    }
 
    public static void main(String[] args) {
        try (ReceiptPrinter p = new ReceiptPrinter("Counter 3")) {
            p.print("Advitha", 640);
            p.print("Navika", 1210);
        }
        System.out.println("Done");
    }
}

Printer opened at Counter 3
Receipt: Advitha, Rs. 640
Receipt: Navika, Rs. 1210
Printer closed at Counter 3
Done

How it works

1. ReceiptPrinter implements AutoCloseable, which has one method: close().
2. try (ReceiptPrinter p = ...) declares the resource in parentheses. When the block ends, normally or through an exception, Java calls p.close() automatically.
3. The cleanup happens at a known point, before "Done", which finalize could never promise.

Files, streams, database connections and sockets in the JDK all implement AutoCloseable, and the later lessons on exceptions and file I/O use them heavily.

Common Mistakes

Relying on finalize or the GC to close files. Close them explicitly with try-with-resources.

Calling System.gc() to "make finalize run". It's only a hint, and the timing is still unpredictable.

Answering "finalize is like a C++ destructor". Destructors run at a known time; finalize may never run.

Interview Corner

Practice

1. Easy: Write a Session class that implements AutoCloseable, prints when it opens and closes, and use it with try-with-resources.
2. Harder: Throw an exception inside the try block of Receipts after the first receipt, and catch it outside. Does close() still run? In which order are the lines printed?

Key Takeaways