innerclass

[senthilkumar74]

Hi,
Im not clear on why the innerclass defined inside a method can access only variable defined final in the outerclass. Would appreciate ur help if some one can throw more light on this!!
------------------
Thanks,
Senthil

[Baskaran Subramani]

Hello Senthil,
ur question is really interesting!!
To make the concept clear, I have created one example. Pls go through this..

public class Outerclass{
       int outer_class_var = 1;
       final int outer_class_final_var = 2;

[B]public void outer_local_method()[/B]{
int local_method_normal_var = 3;
final int local_method_final_var = 4;
 class local_inner_class{
int local_inner_var = 5;
public void local_inner_method(){

int local_inner_class_method_var = local_inner_var * local_method_final_var;
System.out.println("inside local class, var :" + local_inner_class_method_var);

     int x = outer_class_var;
System.out.println("inside local class, free access to enclosing class var  :" + x);
}//end of local inner class's method
}//end of local inner class
  local_inner_class lic = new local_inner_class();
  lic.local_inner_method();
}//end of outer class's member method

public static void main(String[] args){
Outerclass oc = new Outerclass();
oc.outer_local_method();
}//end of main method 
}//end of outer class

In general, A member method in a class can access member variables defined in its body. It holds good for inner class also.in addition to that, Inner classes whose declarations do not occur in a static context may freely refer to the instance variables of their enclosing class. The only problem here is the local variables and member method parameters.
Because the class is inside the method, it can see the local variables in the enclosing method. But it is not physically existing inside the class. so inner class methods can't refer/access these local variables. to tackle this, the compiler creates a hidden copy of the 'final' local variable that the inner class can access safely.
the example illustrated above will give u an output of

inside local var :20
inside local class,free access to enclosing class var :0

hope this would be clear..
Others, pls correct me if I am wrong!!
------
Thanks,
S.Baskaran.


[This message has been edited by Baskaran Subramani (edited September 05, 2000).]

[Sachin Kombrabail]

Hi Guys,
Take a look at this example code
public class Outer
{
final int i = 10;
int j=5;
public void callme()
{
int k=9;
class Inner
{
public void innercalls()
{
System.out.println("i="+i);
System.out.println("j="+j);
System.out.println("k="+k);
}
}
Inner i = new Inner();
i.innercalls();
}
public static void main(String[] argv)
{
Outer o = new Outer();
o.callme();
}
}
If you try and compile this code, you will get a compilation error. The error is not for j which is not defined as final in the outer class but for k which is NOT defined as a final in the method. This means that an inner class which is defined within a method has access to all the variables defined in the outer class but to have access to variables defined within the method these variables have to be defined as final.

[Anonymous]

really...........fantastic and great examples you have given friends.....i am very much impressed with ur examples....they are crystal clear....keep it up!
surya teja
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[senthilkumar74]

Thanks for the explanation. In convinced.

[Anonymous]

RHE has also given a good explanation about accessing variables from an inner class.