Constant in Java

Constant in Java 

• A constant in java is used to map and exact and unchanging value to a variable name.
• Final variables are often declared with static keyword in java and treated as constant.

Final keyword in variable declaration:

Syntax: final datatype v1 = val1, v2=val2,----------------------Vn = Valn;
             Ex: public static final double PI = 3.14159;

Final keyword in method level:

A java method with final keyword is called final method and it cannot be overridden in sub-class.
Syntax:  final returntype methodname(list of formal parameters)
                      {
                                   block of statements;
                       }

               class PersonalLoan{
                     public final String getName(){
                          return "personal loan";
                                                  }
                                      }
                 class CheapPersonalLoan extends PersonalLoan{
                       @override
                     public final String getName(){
                       return "cheap personal loan";
                     // compilation error: overridden final method
                       }

Final keyword in class level:

Java class with final modifier is called final class in java. Final class is complete in nature and cannot be sub-classed or inherited

Several classes in java are final e.g. String, Integer, Double and other wrapper classes.

                            final class PersonalLoan{
                                                                    }

                            class CheapPersonalLoan extends PersonalLoan{
                                       // compilation error: cannot inherit from final class
                                                                     }

Final Keyword allows JVM to optimized method, variable or class.

Few more information on Immutable and Final

• Immutable classes are the one which cannot be modified once it gets created and String is primary example of immutable.
• Immutable classes offer several benefits one of them is that they are effectively read-only and can be safely shared in between multiple threads without any synchronization overhead.
• Final and abstract are two opposite keyword and a final class cannot be abstract in java.
• Final methods are bonded during compile time also called static binding.
• Final variables which is not initialized during declaration are called blank final variable and must be initialized on all constructor either explicitly or by calling this().
• Failure to do so compiler will complain as "final variable (name) might not be initialized".