Java Final Variable

Last Updated : 16 Jan 2026

A final variable can be initialized at the time of declaration or in a constructor, but once assigned, it cannot be modified. The final keyword is used to declare constants. Use the final keyword to declare a variable as final. It is treated as constant.

Syntax:

Characteristics of Final Variables

Once assigned, a final variable cannot be reassigned.
Declaring variable as final does not mean that the variable is immutable; if it is a reference type (like an array or object), its contents can be modified, but the reference cannot be changed.
Final variables must be initialized before use, else a compilation error occurs.

Final Variable Examples

Final Variable as Constant

Example

public class Main {
    public static final double PI = 3.14;
    public static void main(String[] args) {
        // Access the final variable
        System.out.println("Value of PI is: " + PI);
    }
}

Compile and Run

Output:

 
Value of PI is: 3.14

Final Variable in Method as Parameter

Example

public class Main {
    public void printValue(final int num) {
        // num = 10; // This will cause a compilation error
        System.out.println("Value: " + num);
    }
    public static void main(String[] args) {
        Main obj= new Main();
        obj.printValue(77);
    }
}

Compile and Run

Output:

 
Value: 77

Final Variables in Instance Fields

Example

public class Main {
    private final int rollno;
    public Main(int rollno) {
        this.rollno = rollno;
    }
    public void printData() {
        System.out.println("Roll NO: " + rollno);
    }
    public static void main(String[] args) {
        Main obj = new Main(26);
        obj.printData();
    }
}

Compile and Run

Output:

 
Roll NO: 26

Blank Final Variable

A blank final variable in Java is a final variable that is declared but not initialized at the time of declaration. Again, once a final local variable has been initialized, it cannot be set, and any attempts to assign a value to blankfinal result in a compile-time error.

Important Points to Remember

A blank final variable must be initialized before the constructor completes; otherwise, the compiler will throw an error.
If there are more than one constructor, the blank final variable must be initialized in each constructor.
Blank final variables are useful when the value needs to be set dynamically during object creation.

Example of Blank Final Variable

Example

class Main {
    // Declaring a blank final variable
    final int cost;
    // Initializing the blank final variable in the constructor
    Main (int value) {
        cost = value;
    }
    void display() {
        System.out.println("Value of goods: " + cost);
    }
    public static void main(String[] args) {
        Main obj = new Main(5000);
        obj.display(); 
    }
}

Compile and Run

Output:

 
Value of goods: 5000

Conclusion

Overall, the final keyword in Java provides a powerful mechanism for enhancing code robustness, security, performance, and maintainability by enforcing immutability, preventing unintended modifications, and enabling compiler optimizations.

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