Java Final Keyword
- A java variable can be declared using the keyword final. Then the final variable can be assigned only once.
- A variable that is declared as final and not initialized is called a blank final variable. A blank final variable forces the constructors to initialise it.
- Java classes declared as final cannot be extended. Restricting inheritance!
- Methods declared as final cannot be overridden. In methods private is equal to final, but in variables it is not.
- final parameters – values of the parameters cannot be changed after initialization. Do a small java exercise to find out the implications of final parameters in method overriding.
- Java local classes can only reference local variables and parameters that are declared as final.
- A visible advantage of declaring a java variable as static final is, the compiled java class results in faster performance.
A discussion inviting controversy on java final keyword:
‘final’ should not be called as constants. Because when an array is declared as final, the state of the object stored in the array can be modified. You need to make it immutable in order not to allow modifcations. In general context constants will not allow to modify. In C++, an array declared as const will not allow the above scenario but java allows. So java’s final is not the general constant used across in computer languages.
A variable that is declared static final is closer to constants in general software terminology. You must instantiate the variable when you declare it static final.
Definition as per java language specification (third edition) – 4.12.4 is “A final variable may only be assigned to once.”(§4.1.2)
Java language specification tries to redefine the meaning of constant in the following way!
We call a variable, of primitive type or type String, that is final and initialized with a compile-time constant expression (§15.28) a constant variable. Whether a variable is a constant variable or not may have implications with respect to class initialization (§12.4.1), binary compatibility (§13.1, §13.4.9) and definite assignment (§16).