Final variables in Java

 

🔷 Final Variables in Java

✅ What is final in Java?

The final keyword is used to declare constants. Once assigned, a final variable's value cannot be changed.

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📌 Types of Final Usage:

1. Final variable

2. Final method

3. Final class

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✅ 2.1 Final Variable

• Value is assigned only once.

• If not initialized during declaration, it must be initialized in a constructor or static block.

🔹 Example:

class Circle {
    final double PI = 3.14159;  // constant

    double area(double r) {
        return PI * r * r;
    }
}

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✅ 2.2 Final Method

• Cannot be overridden by subclasses.

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

class B extends A {
    // void show() {} ❌ Compilation error
}

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✅ 2.3 Final Class

• Cannot be extended (no subclassing).

final class Animal {
    void sound() {
        System.out.println("Animal sound");
    }
}

// class Dog extends Animal {} ❌ Error: Cannot inherit from final class