Java Final Variables - final Keyword with Variables

⏱️ 8 min read • Beginner Level • Lesson 18

A final variable in Java is a variable whose value cannot be changed after it has been assigned. The final keyword is commonly used to create constants and to prevent accidental value modification.

Before learning final variables, you should understand Java variables, Java data types, and Java naming conventions.

What is a Final Variable in Java?

A variable declared with the final keyword is called a final variable. Once a value is assigned to a final variable, it cannot be reassigned.

Syntax of Final Variable

The basic syntax of a final variable is:

final dataType variableName = value;

Example:

final int MAX_MARKS = 100;
final double PI = 3.14159;
final String APP_NAME = "ProwessApps";

Final Variable Example

In this example, MAX_MARKS stores a fixed value. We can use it in calculations, but we cannot change it later.

public class FinalVariableExample {
    public static void main(String[] args) {
        final int MAX_MARKS = 100;
        int obtainedMarks = 85;

        System.out.println("Obtained Marks: " + obtainedMarks);
        System.out.println("Maximum Marks: " + MAX_MARKS);
    }
}

Output:

Obtained Marks: 85
Maximum Marks: 100

Can a Final Variable be Changed?

No. Once a final variable gets a value, it cannot be changed. If you try to assign a new value, Java shows a compilation error.

public class FinalReassignError {
    public static void main(String[] args) {
        final int age = 20;

        // age = 25; // Error: cannot assign a value to final variable age

        System.out.println(age);
    }
}

Final Local Variable

A final local variable is declared inside a method, constructor, or block. It must be assigned before it is used and cannot be changed after assignment.

public class FinalLocalVariable {
    public static void main(String[] args) {
        final String courseName = "Java Programming";
        System.out.println(courseName);
    }
}

Output:

Java Programming

Final Instance Variable

A final instance variable belongs to an object. Once initialized, it cannot be changed for that object. It can be initialized directly or inside a constructor.

public class FinalInstanceVariable {
    final int rollNumber;

    FinalInstanceVariable(int rollNumber) {
        this.rollNumber = rollNumber;
    }

    void showRollNumber() {
        System.out.println("Roll Number: " + rollNumber);
    }

    public static void main(String[] args) {
        FinalInstanceVariable student = new FinalInstanceVariable(101);
        student.showRollNumber();
    }
}

Output:

Roll Number: 101

Blank Final Variable

A blank final variable is a final variable that is declared without assigning a value immediately. It must be initialized before the constructor finishes.

public class BlankFinalVariable {
    final String studentName;

    BlankFinalVariable(String name) {
        studentName = name;
    }

    public static void main(String[] args) {
        BlankFinalVariable student = new BlankFinalVariable("Ayan");
        System.out.println(student.studentName);
    }
}

Output:

Ayan

static final Variable in Java

A static final variable belongs to the class and cannot be changed. It is commonly used to create constants.

public class StaticFinalVariable {
    static final double PI = 3.14159;

    public static void main(String[] args) {
        System.out.println("PI: " + PI);
    }
}

Output:

PI: 3.14159

Real-World Use of static final Constants

Final Reference Variable

If a reference variable is declared as final, the reference cannot point to another object. However, the data inside the object may still be changed if the object is mutable.

class Student {
    String name;
}

public class FinalReferenceVariable {
    public static void main(String[] args) {
        final Student student = new Student();
        student.name = "Ayan";

        System.out.println(student.name);

        // student = new Student(); // Error: cannot assign a new object to final reference
    }
}

Output:

Ayan

Final Variable vs Normal Variable

Difference Between final, static and static final

Common Mistakes with Final Variables

Frequently Asked Questions

🧠 Test your understanding with a quick quiz

class Student {
    String name;
}

public class Test {
    public static void main(String[] args) {
        final Student s = new Student();
        s.name = "Ayan";
        System.out.println(s.name);
    }
}

public class Test {
    static final double PI = 3.14;

    public static void main(String[] args) {
        System.out.println(PI);
    }
}

public class Test {
    public static void main(String[] args) {
        final int marks = 90;
        System.out.println(marks);
    }
}

🎉 Great job! Continue learning Java step by step.