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Using Final in method parameters

6 replies on 1 page. Most recent reply: Dec 10, 2003 2:11 AM by Jonathon Brozny

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sudheesh

Posts: 4
Nickname: sudhee
Registered: Dec, 2003

Using Final in method parameters Posted: Dec 9, 2003 2:47 AM
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Hi ,

whats the exact difference between the follwing two methods

public void showValue(int i)

public void showValue(final int i)


Jonathon Brozny

Posts: 24
Nickname: jonathon
Registered: Oct, 2003

Re: Using Final in method parameters Posted: Dec 9, 2003 7:24 AM
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With (final int i) i cannot be reassigned. Its a constant.

Senthoorkumaran Punniamoorthy

Posts: 335
Nickname: senthoor
Registered: Mar, 2002

Re: Using Final in method parameters Posted: Dec 9, 2003 7:28 AM
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Check the heading New Uses for final in this url.

http://java.sun.com/docs/books/tutorial/post1.0/converting/languageChanges.html

public class Util {
 
  public static void testing(final int x){
    x=25;
  }
  public static void testing1(int x){
    x=25;
  }
 
  public static void main(String[] args) {
    int x = 20;
    testing(x);
    testing1(x);
  }
}


in the method testing its illegal to change the value of x since its declared final, a final variable once assigned cannot be changed. And this will be flagged at compile time.

sudheesh

Posts: 4
Nickname: sudhee
Registered: Dec, 2003

Re: Using Final in method parameters Posted: Dec 9, 2003 11:00 PM
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Thanx for the url.It was helpful.
but it says
"You can defer initialization of a final field or variable"
but is that possible?
The final variable needs to be initiated when it is declared.
For example this file wont compile.
public class Util {
final int a;
}
Can u pls give me an example of deferreed initialization?

Jonathon Brozny

Posts: 24
Nickname: jonathon
Registered: Oct, 2003

Re: Using Final in method parameters Posted: Dec 10, 2003 12:22 AM
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You have to initialize finals in the constructor. This give you a little more flexability because each object can have a different value for that field.

public class Util {
	final int a;
 
	Util (int somevalue){
		a = somevalue;
	}
}

sudheesh

Posts: 4
Nickname: sudhee
Registered: Dec, 2003

Re: Using Final in method parameters Posted: Dec 10, 2003 12:35 AM
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Ok.That was heplful.
and just one more clarification needed.
For every method which has a parameter [which wont be changed anyway]if i use final keyword then that would really increase the performance a bit.Am i right?

Then y is it that we dont normally do it in most of the code?

Jonathon Brozny

Posts: 24
Nickname: jonathon
Registered: Oct, 2003

Re: Using Final in method parameters Posted: Dec 10, 2003 2:11 AM
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If it is a compile time constant then the compiler will make some optimizations.

I don't know that "we" don't use it "normally". I don't use it normally because I normally don't have a lot of constant values. But it does depend on what you are working on for how often you would use it I guess.

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