Final

tags : Java

The final keyword in java is used to restrict the user. The java final keyword can be used in many context. Final can be:

1. variable → stop value change
2. method → stop overriding
3. class → stop inheritance

If you want to create a variable that is initialized at the time of creating object and once initialized may not be changed, it is useful. For example PAN CARD number of an employee. If you try to modify, you get Output: Compile Time Error

1. Can we initialize blank final variable?

Yes, but only in constructor.

class Bike10{  
	final int speedlimit;//blank final variable  
	
	Bike10(){
		speedlimit=70;
		System.out.println(speedlimit);  
	}
}

Static blank final variable

A static final variable that is not initialized at the time of declaration is known as static blank final variable. It can be initialized only in static block.

Example of static blank final variable

class A{  
	static final int data;//static blank final variable  
	static{ 
		data=50;
	}  
   public static void main(String args[]){  
     System.out.println(A.data);  
	}  
}

What is the final keyword in Java?

The final keyword is used to declare constants or prevent changes. It can be applied to:

• Variables

• Methods

• Classes

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What does a final variable mean?

A final variable is a constant. Once it is assigned a value, it cannot be changed.

final int MAX = 100;

Attempting to reassign will cause a compile-time error.

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Can a final variable be uninitialized?

Yes, but only if it’s:

• A blank final (assigned in constructor)

• A static final (assigned in static block)

final int age;
age = 25; // allowed if done once

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What is a final method in Java?

A method declared final cannot be overridden by subclasses.

class A {
    final void display() { }
}
 
class B extends A {
    // void display() {} ❌ — Not allowed
}

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Why would you use a final method?

To prevent subclasses from changing the behavior of critical methods (e.g., utility or security logic).

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What is a final class in Java?

A final class cannot be subclassed.

final class Shape { }
 
class Circle extends Shape { } // ❌ Error

Example: java.lang.String is a final class.

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Can a final variable refer to a mutable object?

Yes. A final reference means you cannot change the reference, but you can modify the object it points to.

final List<String> list = new ArrayList<>();
list.add("Java"); // allowed
list = new ArrayList<>(); // ❌ not allowed

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What is the difference between final, finally, and finalize()?

Term	Meaning
final	Prevents modification (variable, method, class)
finally	Block that always executes in a try-catch
finalize()	Method called by GC before object is destroyed (deprecated)

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Can a final method be static?

Yes. A method can be both static and final.

public static final void show() { }

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Can a final variable be initialized inside a constructor?

Yes. A blank final instance variable must be initialized in every constructor.

final int x;
MyClass() {
    x = 5;
}

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What is the use of static final variables?

They are used to create constants shared across all instances.

public static final double PI = 3.14;

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What happens if you try to override a final method?

The compiler throws an error:

“Cannot override the final method from superclass.”

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Why should final be used for constants?

It ensures read-only behavior, improves code safety, and helps the compiler optimize performance.

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Can a final class implement an interface?

Yes. A final class can implement an interface but cannot be extended.

final class MyService implements Runnable {
    public void run() { }
}

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Can constructors be final?

No. Constructors cannot be final because they are never inherited or overridden.

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Can an abstract class or method be final?

No. Abstract means “must be overridden”, while final means “cannot be overridden” — so they are opposites.

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Can a method be final and synchronized?

Yes. A method can be both final and synchronized.

public final synchronized void process() { }

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What are the benefits of using final in Java?

• Ensures immutability

• Prevents accidental inheritance or overrides

• Helps compiler with optimizations

• Improves thread safety when used with immutable objects

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How does the final keyword affect performance?

In some cases, the JVM can optimize final methods and variables better because it knows they won’t change.