Constant – What is Constant? Type of Constant

Constants: Constants in java are fixed values those are not changed during the Execution of program. A literal is a constant value that can be classified as integer literals, string literals and boolean literals. To make a static field constant in Java, make a variable as both static and final. java supports several types of Constants  those are  

Integer Constants:  Integer Constants refers to a Sequence of digits which Includes only negative or positive Values and many other things those are as follows

• An Integer Constant must have at Least one Digit.
• it must not have a Decimal value.
• it could be either positive or Negative.
• if no sign is Specified then it should be treated as Positive.
• No Spaces and Commas are allowed in Name.

Real Constants:

• A Real Constant must have at Least one Digit.
• it must have a Decimal value.
• it could be either positive or Negative.
• if no sign is Specified then it should be treated as Positive.
• No Spaces and Commas are allowed in Name.

Like 251, 234.890 etc are Real Constants.

In The Exponential Form of Representation the Real Constant is Represented in the two Parts The part before appearing e is called mantissa whereas the part following e is called Exponent.

• In Real Constant The Mantissa and Exponent Part should be Separated by letter e.
• The Mantissa Part have may have either positive or Negative Sign.
• Default Sign is Positive.

Single Character Constants

A Character is Single Alphabet a single digit or a Single Symbol that is enclosed within Single inverted commas.

Like ‘S’ ,’1’ etc are Single  Character Constant.

String Constants:  String is a Sequence of Characters Enclosed between double Quotes These Characters may be digits ,Alphabets  Like “Hello” , “1234” etc.

Backslash Character Constants: Java Also Supports Backslash Constants those are used in output methods For Example \n is used for new line Character These are also Called as escape Sequence or backslash character Constants For Ex:    

\t  For Tab  ( Five Spaces in one Time ).

\b Back Space etc.

final Variable (OR Constant Variable)

Variables are useful when you need to store information that can be changed as program runs. However, there may be certain situations in the program in which the value of variable should not be allowed to modify. This is accomplished using a special type of variable known as final variable. The final variable also called constant variable. It is a variable with a value that cannot be modified during the execution of the program.

To declare a final variable, use the final keyword before the variable declaration and initialize it with a value. Its syntax is

final datatype varName = value;

For example:

final double PI = 3.141592;

This statement declares a variable PI of type double which is initialized to 3.141592, that cannot be modified. If an attempt is made to modify a final variable after it is initialized, the compiler issues an error message “cannot assign a value to final variable PI”.

You can also defer the initialization of final variable, such a final variable is know as blank final. However, it must be initialized before it is used.
Final variables are benefitical when one need to prevent accidental change to method parameters and with variables accessed by anonymous class.
Now consider a program to calculate the area of the circle,

//Area of the circle
public class AreaCircle {
    public static void main(String[] args) {
        int r = 10; // initializing radius
        final double PI = 3.141592 //final variable
        double area;
        //PI = 3.142; will generate an error
        area = PI * r * r;
        System.out.println(“Area of circle is –>” +area);
     }
}
Output: Area of circle is — >314.1592
NOTE: It is recommended to declare a final variable in uppercase