Constant & Literals in Java

Constants:

• A constant is a variable whose value cannot change once it has been assigned. 
• Java doesn't have built-in support for constants.
• It has special two-variable modifiers...such as static and final.

1. Static Modifier:

• Static is used without first creating an instance of the class.
• Example: main() method.
• main() method doesn't need any object.
• main() method is executed for every program and declared as static.
• A static class member is associated with the class itself, rather than an object. All class instances share the same copy of the variable.
• Syntax: static datatype variable = value;
• Example: static int book = 101;

2. Final Modifier

• The final modifier means that the variable's value cannot change. 
• Once the value is assigned, it cannot be reassigned. 
• Primitive data types can be declared using the final modifier.
• Syntax:  final datatype variable_name = value;
• Example:  final int myNum = 15;

Difference between Static Vs Final

• 1. Static define by static & final define by final keyword.
• 2. Final variable become constant & static variable become common to all object in the given class.
• 3. The final variable cant be processed in the inherited class while static variable same for each object in the given class.
• 4. The final variable value cant be change & static variable can set the default value but can be reinitialized.

Java Program

Literals:

• Any constant value which can be assigned to the variable is called as literal/constant.
• Syntax: datatype variable_name = value;
• Example: int x = 100; 

• 1. Integral literals
• 2. Floating-Point literal
• 3. Char literal
• 4. String literal
• 5. boolean literals

1. For Integral data types.

• For Example byte, short, int, long
• A. Decimal literals (Base 10):
• In this form, the allowed digits are 0-9.
• Example: int x = 101;
• B. Octal literals (Base 8): 
• In this form, the allowed digits are 0-7.
• Example: int x = 0146; // The octal number should be prefix with 0.
• C. Hexa-decimal literals (Base 16): 
• In this form, the allowed digits are 0-9 and characters are a-f. 
• We can use both uppercase and lowercase characters. 
• Here, java is not case-sensitive (with 0X or 0x).
• Example: int x = 0X123Face;  // The hexadecimal number should be prefix
• D. Binary literals: 
• With JDK 1.7 onward we can specify binary literals value.
• In this form allowed digits are 0 and 1. 
• Literals value should be prefixed with 0b or 0B.
• Example: int x = 0b1111;

Example:

int a = 101; // decimal-form literal 

        int b = 0100; // octal-form literal 

        int c = 0xFace; // Hexa-decimal form literal 

        int d = 0b1111; // Binary literal 

        System.out.println(a); 

        System.out.println(b); 

        System.out.println(c); 

        System.out.println(d);

2. Floating-Point literal

• For Example float, double

  float a = 101.230; // decimal-form literal 

        float b = 0123.222; // It also acts as decimal literal 

        float c = 0x123.222; // Hexa-decimal form 

        System.out.println(a); 

        System.out.println(b); 

        System.out.println(c);

3. char literal:

• A. Single quote: 
• single character within a single quote.
• Example:char ch = 'a';

• B. Char literal as Integral literal: 
• Char literal as integral literal which represents Unicode value.
• It can be either in Decimal, Octal and Hexadecimal forms. 
• It allowed range is 0 to 65535.
• Example: char ch = 062;

• C. Unicode Representation:
• Char literals in Unicode representation ‘\uxxxx’. 
• Here 'xxxx' represents 4 hexadecimal numbers.
• Example: char ch = '\u0061';

• D. Escape Sequence: 
• Every escape character can be specify as char literals.
• Example: char ch = '\n';

Example:

char ch = 'a'; // signle character literl within signle quote 

        char b = 0789; // It is an Integer literal with octal form 

        char c = '\u0061'; // Unicode representation 

        System.out.println(ch); 

        System.out.println(b); 

        System.out.println(c); 

        // Escape character literal 

        System.out.println("\"  is a symbol"); 

4. String literal

• Any sequence of characters within double quotes is treated as String literals.
• Example: String s = "Hello";

5. boolean literal

• Only two values are allowed for Boolean literals i.e. true and false.
• Example: boolean b = true;

Example: 

boolean b = true; 

        boolean c = false; 

        boolean d = 0; 

        boolean b = 1; 

        System.out.println(b); 

        System.out.println(c); 

        System.out.println(d); 

        System.out.println(e);