"final" keyword in java (constant in java using "final" Keyword)

Constants in Java:

·         A constant is an identifier whose value will not be changed during the execution of the program.

·         To make a constant in Java, we must use a reserved keyword called “final”.

·         The “final” keyword plays important roles at 3 places. They are:

• At variable level
• At method level
• At class level

• “final” at variable level:

• When we don’t want to change the value of a variable, that variable must be made as final variable.
• Java allows us to declare a final variable and to initialize it later.
• The “final” variable declaration: when the final variable id declared, one time assignment/initialization is possible and no further modification and assignment are possible.
• Syntax:

final data-type varName1;

varName1 = val1;

o   Java allows us to declare cum initialize a final variable.

§  When a final variable is declared and initialized then no immediate modifications and assignments are possible.

§  Syntax:

final data-type varName1 = value1;

o   Hence, the final variable value can’t be changed or modified.

• “final” at method level:

• When we don’t want to change the definition of a method, that method must be made as final.
• Syntax:

final returnType methodName(param, if any)

{

            Block of statements

}

o   For example:

Public final float calculateInterest(float p, float r, float t)

{

            return ((p*r*t)/100);

}

o   The definition which is provided in calculateInterest() is fixed i.e. we can’t change it since method is declared as final but we can reuse the method.

o   Hence, the final method can’t be overridden or redifined.

• “final” at class level:

• When we don’t want to inherit a class into any other class, then that class must be made as final.
• Syntax:

final class <ClassName>

{

            Variable declaration

            Method definitions

}

o   For example:

final class C1

{

            int a, b, c;

            public void f1()

            {

                        Block of statements

}

---------------------

---------------------

}

o   Once the class is declared as final, its data members and member methods become final.

o   class C2 extends C1 // Invalid statement.

o   Hence, final class can’t be inherited or reused or extended.

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