A Named Constant is an identifier that represents a permanent value. The value of a variable may change during the execution of a program; but a Named Constant (or just Constant) represents permanent data that never changes (for example, π is a constant) depending on the type of Java “constant”.
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Final vs. Static Final
There are 2 types of Java “constants”. final
and static final
. The syntax for declaring the lone final
constant is:
final datatype CONSTANTNAME = value;
The lone final
constant only forces a variable value to be permanent in a single class instance.
The syntax for declaring static final
is:
static final datatype CONSTANTNAME = value;
The constants static final
forces a variable value to be permanent in all class instances.
Example
A Java named constant can be declared and initialized in the same statement or in separate statements. The word final
is a Java keyword for declaring a constant. For example:
import java.util.Scanner; // Scanner is in the java.util package public class ComputeAreaWithConstant { public static void main(String[] args) { final double PI = 3.14; // Declare a constant // Make a Scanner Object Scanner input = new Scanner(System.in); // Prompt the user to enter a radius System.out.print("Enter a number for radius: "); double radius = input.nextDouble(); // Compute area double area = radius * radius * PI; // Display results System.out.println("The area for the circle of radius " + radius + " is " + area); } }
Let’s say that in the above example you add the statement:
double PI = 5.56;
to re-assign the value of PI. But the benefit of using the constant declaration final
is that the Java program will not allow you to change the value of a constant:
Another benefit is that you only have to change the value of the constant from a single location.