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home / developersection / forums / what is the significance of the final keyword when applied to classes, methods, and variables?
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What is the significance of the final keyword when applied to classes, methods, and variables?

Anubhav Sharma 433 18 Jul 2024

What is the significance of the final keyword when applied to classes, methods, and variables?

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Updated 18 Jul 2024
Anubhav Sharma
Anubhav Sharma

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The Anubhav portal was launched in March 2015 at the behest of the Hon'ble Prime Minister for retiring government officials to leave a record of their experiences while in Govt service .

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1 Answers

Ravi Vishwakarma
Ravi Vishwakarma 18 Jul 2024
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The final keyword in Java can be applied to classes, methods, and variables, and it serves different purposes in each context. Here is an explanation of its significance:

1. Final Classes

When a class is declared as final, it cannot be subclassed. This means no other class can extend a final class.

Significance:

  • Security: Prevents inheritance, which can be useful when creating immutable classes or ensuring the integrity of a class's behavior.
  • Performance: The JVM can optimize calls to final classes more effectively because it knows that the class will not be extended.

Example:

public final class ImmutableClass {
    private final int value;

    public ImmutableClass(int value) {
        this.value = value;
    }

    public int getValue() {
        return value;
    }
}

// This will cause a compile-time error
// public class SubClass extends ImmutableClass {}

2. Final Methods

When a method is declared as final, it cannot be overridden by subclasses.

Significance:

  • Consistency: Ensures that the method's behavior remains unchanged across all subclasses.
  • Security: Prevents subclasses from altering crucial methods, maintaining the integrity of the class's behavior.
  • Performance: The JVM can optimize calls to final methods more effectively.

Example:

public class ParentClass {
    public final void show() {
        System.out.println("This is a final method.");
    }
}

public class ChildClass extends ParentClass {
    // This will cause a compile-time error
    // public void show() {}
}

3. Final Variables

When a variable is declared as final, its value cannot be changed once it is initialized, this applies to instance, static, and local variables.

Significance:

  • Constants: Useful for defining constants. A final variable acts as a constant whose value is set once and cannot be modified.
  • Immutability: Helps create immutable objects by ensuring that the state cannot be changed after construction.
  • Thread Safety: Reduces data corruption risks in concurrent applications by ensuring that the value remains constant after initialization.

Example:

public class Constants {
    public static final double PI = 3.14159;

    public static void main(String[] args) {
        final int fixedValue = 10;

        // This will cause a compile-time error
        // fixedValue = 20;
    }
}

the final keyword appropriately, developers can create more secure, reliable, and optimized Java applications.

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