What is final in Java?

What is final in Java?

Final is the modifiers applicable for classes, methods, and variables. 

• The main advantage of final keyword is we can achieve security and we can provide the unique implementation.
• Final keyword improves performance. Not just JVM can cache final variable but also application can cache frequently use final variables.
• Final variables are safe to share in multi-threading environment without additional synchronization overhead.
• But the main disadvantage of a Final keyword is we are missing key benefits of OOPS.

 

Final Method

1. Whatever method parent has by default available to child throw inheritance.
2. If the child not satisfied with parent method implementation then the child is allowed to redefine the method based on its requirement. This process is called overriding.
3. If the parent class method is declared as final then we can’t override that method in child class because its implementation is final.
4. A final method cannot be overridden

 

Final Class

1. If a class declared as final we can’t extend the functionality of that class ie we can’t create the child class for that class ie inheritance is not possible for final classes.
2. Every method present in the final class is always final by default but every variable present inside final class need not be final.
3. The other use of final with classes is to create an immutable class like the predefined String class. You can not make a class immutable without making it final.
4. A final class cannot be subclassed

 

Final Instance Variable

1. If the value of the variable is varied from object to object such type of variables is called instance variables.
2. For every object, a separate copy of instance variables will be created.
3. For instance variable, we are not required to perform initialization explicitly. JVM will always provide default values(Zero).
4. If the instance variable declared as final then compulsory we have to perform initialization explicitly. Whether we are using or not and JVM won’t provide default values.
5. The only difference between a normal variable and a final variable is that we can re-assign value to a normal variable but we cannot change the value of a final variable once assigned.
6. Final variables are nothing but constants. We cannot change the value of a final variable once it is initialized.

Rule:-

1. For final instance variable compulsory, we should perform initialization before constructor completion. i.e. The following are various places for initialization.
   1. At the time of declaration.
   2. Inside instance block
   3. Inside constructor.
2. These are the only possible place to perform initialization for the final instance variable. If we are trying to perform initialization anywhere else then we will get compile time error.