Q: What is the difference between final, finally, and finalize?

Answer:

Despite the similar names, these are completely unrelated concepts.

final — A Keyword for Immutability/Restriction

1. final variable — Value cannot be changed after assignment (constant).

final int MAX = 100;
MAX = 200; // ❌ Compilation error

2. final method — Cannot be overridden by subclasses.

public class Parent {
    public final void doWork() { /* cannot be overridden */ }
}

3. final class — Cannot be extended (no subclasses).

public final class String { /* no one can extend String */ }

4. final with references — The reference can't change, but the object it points to CAN.

final List<String> list = new ArrayList<>();
list.add("hello");       // ✅ Modifying the object is fine
list = new ArrayList<>(); // ❌ Reassigning the reference is not

finally — Exception Handling Block

A block that always executes after a try-catch, whether an exception occurred or not. Used for cleanup (closing resources, releasing locks).

try {
    riskyOperation();
} catch (Exception e) {
    log.error("Failed", e);
} finally {
    connection.close(); // Always runs, even if exception is thrown
}

[!WARNING] finally does NOT execute in two edge cases:

1. System.exit() is called in the try/catch block.
2. The JVM crashes or the thread is killed.

finalize() — Garbage Collection Hook (DEPRECATED)

A method called by the garbage collector before destroying an object. It was intended for cleanup of native resources.

@Override
protected void finalize() throws Throwable {
    // Cleanup before GC — DON'T USE THIS
    super.finalize();
}

Why it's deprecated (Java 9+):

• No guarantee when (or if) it will be called.
• Causes significant GC performance overhead.
• Objects can be "resurrected" in finalize(), creating bugs.
• Not a replacement for proper resource management.

Use instead: try-with-resources + AutoCloseable, or Cleaner (Java 9+).

Summary