Difference between Private and Final

[Naty wills]

Hi all,
I am confused abt the use of Final and private keyword in java.
Are both use to prevent overridding??

[Ernest Friedman-Hill]

The purpose of "private" is to promote encapsulation. Member variables should almost always be private; class A should not be trying to touch the member data of class B.

"final" has a few different meanings. Applied to a variable, it prevents changes to the variable after initialization, making it a "constant." Applied to a method, it does, indeed, prevent overriding. Applied to a class, it prevents the class from being extended. All of these meanings have something in common: they allow the programmer to have fairly strong beliefs about the value or purpose of something. If you know a class can never be extended, then you know for sure how an instance of the class will behave -- you know you're not dealing with a subclass that changes something, since you know no subclasses can exist. This helps with both engineering and security.
[ September 05, 2006: Message edited by: Ernest Friedman-Hill ]

[Burkhard Hassel]

Hi all,
This is about final/private in methods only.

final does not allow overriding of methods. If you do, you'll get a compiler error.

private methods are not visible outside their classes. So when you extend a class, you can give a method the same declaration as in the upper class. It is a redefinition (no override!) with no relation to the upper class method.
Especially no polymorphism.
Example

class Main {
public static void main(String[] args) {
Alpha a = new Alpha();
Beta  b = new Beta();
Alpha mix = new Beta();
a.bar();
b.bar();
mix.bar();
}
}
 
class Alpha {
private void foo() {
System.out.println("ALPHA");
}
public void bar(){
// show foo to the outer world
foo();
}
}
 
class Beta extends Alpha {
public void foo() {
System.out.println("BETA");
}
// no need for bar, it's inherited
}

The bar method is only necessary to call foo from outside its class.


Outputs 3* ALPHA
Remove the private (-> default public or protected) and you'll have polymophic output.
make it final (in class Alpha), you'll get a compiler error in class Beta.


Yours,
Bu.



ps: upper class methods can also be wearing large hats at a horse race or polo match.

[Naty wills]

Thanks a lot for prompt answers..
Now all my doubts are cleared..

[supriya riya]

This explanation helped a lot.

[S Nirmal]

difference between private and final method helped a lot. Thank you.

[Campbell Ritchie]

Welcome to the Ranch

It is nice to think that these old posts can still be useful.