final vs finally vs finalize()

This is a classic Java interview question that tests understanding of keywords, exception handling, and garbage collection. Though they sound similar, they serve completely different purposes.

High-Level Difference (One Line)

• final → Prevents change (variables, methods, classes)
• finally → Ensures execution of cleanup code
• finalize() → Cleanup before garbage collection (deprecated)

1️⃣ final Keyword

What Is final?

final is a keyword used to restrict modification.

It can be applied to:

• Variables
• Methods
• Classes

final Variable

final int x = 10;
x = 20; // ❌ compile-time error
          

• ✔ Value cannot be changed
• ✔ Used for constants

final Method

class Parent {
    final void show() {}
}
class Child extends Parent {
    // void show() {} ❌ cannot override
}
          

• ✔ Prevents method overriding

final Class

final class Utility {}
class Test extends Utility {} // ❌ not allowed
          

• ✔ Prevents inheritance
• ✔ Used for immutability (String)

2️⃣ finally Block

What Is finally?

finally is a block used with try–catch to execute important cleanup code.

✔ Executes always (almost)

Syntax

try {
    // risky code
} catch (Exception e) {
    // handling
} finally {
    // cleanup code
}
          

Example

try {
    int a = 10 / 0;
} catch (ArithmeticException e) {
    System.out.println("Exception");
} finally {
    System.out.println("Always executes");
}
          

✔ Executes whether exception occurs or not

When finally Does NOT Execute (Interview Trap)

• System.exit()
• JVM crash
• Power failure

3️⃣ finalize() Method

What Is finalize()?

finalize() is a method of the Object class that is called by the Garbage Collector before object destruction.

protected void finalize() throws Throwable {
    // cleanup
}
          

Example

class Test {
    protected void finalize() {
        System.out.println("Finalize called");
    }
}
          

• ✔ Called before garbage collection
• ❌ Not guaranteed when or if it runs

Important Note (Modern Java)

• ⚠ finalize() is deprecated (Java 9+)
• ✔ Unreliable
• ✔ Performance issues
• ✔ Use try-with-resources / AutoCloseable instead

finalize() vs Cleanup (Modern Practice)

❌ Avoid:

finalize()
          

✔ Prefer:

try-with-resources

try (FileInputStream fis = new FileInputStream("a.txt")) {
    // use resource
}
          

Side-by-Side Comparison (Interview Favorite)

Common Interview Traps

• Confusing finally with finalize()
• Thinking finalize() always runs
• Assuming finally executes after System.exit()
• Believing final makes objects immutable (only references)

Interview-Ready Answers

Short Answer

final restricts modification, finally ensures execution of cleanup code, and finalize() is called by the garbage collector before object destruction.

Detailed Answer

In Java, final is a keyword used to restrict inheritance, overriding, or reassignment. finally is a block associated with exception handling that executes regardless of whether an exception occurs. finalize() is a method of the Object class that was intended for cleanup before garbage collection, but it is deprecated due to unpredictability.

Key Takeaway

final → restriction
finally → guaranteed execution
finalize() → unreliable, deprecated
Mastering this distinction is mandatory for Core Java interviews and demonstrates strong fundamentals.