ELEMENTARY PROGRAMMING - Introduction to Java Programming: Comprehensive Version - page 43

illegal, because the data type of x is int . You cannot assign a double value ( 1.0 ) to
an int variable without using type casting. Type casting is introduced in Section 2.15.

2.6

✓ ✓

Identify and fix the errors in the following code:

Check

Point

1 public class Test {
2 public static void main (String[] args) {
3 int i = j = k = 2 ;
4 System.out.println(i + "" + j + "" + k);
5 }
6 }

2.7 Named Constants
A named constant is an identifier that represents a permanent value.

Key
Point
constant

The value of a variable may change during the execution of a program, but a named con-
stant, or simply constant , represents permanent data that never changes. In our ComputeArea
program, p is a constant. If you use it frequently, you don't want to keep typing 3.14159 ;
instead, you can declare a constant for p . Here is the syntax for declaring a constant:

final datatype CONSTANTNAME = value;

A constant must be declared and initialized in the same statement. The word final is
a Java keyword for declaring a constant. For example, you can declare p as a constant and
rewrite Listing 2.1 as in Listing 2.4.

final keyword

L ISTING 2.4

ComputeAreaWithConstant.java
1 import java.util.Scanner; // Scanner is in the java.util package
2
3 public class ComputeAreaWithConstant {
4 public static void main(String[] args) {

5 final double PI = 3.14159 ; // Declare a constant

6
7 // Create a Scanner object
8 Scanner input = new Scanner(System.in);
9
10 // Prompt the user to enter a radius
11 System.out.print( "Enter a number for radius: " );
12

double radius = input.nextDouble();

13
14 // Compute area

15 double area = radius * radius * PI;

16
17 // Display result
18 System.out.println( "The area for the circle of radius " +
19 radius + " is " + area);
20 }
21 }

There are three benefits of using constants: (1) you don't have to repeatedly type the same
value if it is used multiple times; (2) if you have to change the constant value (e.g., from 3.14
to 3.14159 for PI ), you need to change it only in a single location in the source code; and
(3) a descriptive name for a constant makes the program easy to read.

benefits of constants