Constants

1. What is a Constant?

A constant is a value that, once assigned, cannot be changed during the program's execution. In Java, you create a constant using the final keyword along with a variable declaration.

2. Why is it used?

Constants protect important fixed values, like a tax rate or the number of days in a week, from being accidentally changed somewhere else in the code. This makes programs safer and easier to maintain.

3. Real-Life Example

Think of your date of birth. It is a fixed fact that never changes no matter what happens in your life afterward. A constant in Java behaves the same way — fixed once, and never modified again.

4. Syntax

java
final dataType CONSTANT_NAME = value;

5. Example Program

java
public class ConstantDemo {
    public static void main(String[] args) {
        final double TAX_RATE = 0.18;
        double price = 1000;
        double finalPrice = price + (price * TAX_RATE);
        System.out.println("Final Price: " + finalPrice);
    }
}

Output:

Final Price: 1180.0

6. Key Points to Remember

• Constants use the final keyword and, by convention, are named in UPPERCASE.
• Trying to reassign a final variable causes a compile-time error.
• Constants make code more readable by giving meaning to fixed values.