Inner Class inside a method

[Mark Henryson]

Hi,

I am trying to access the variable inside the method by the Inner Class object inside the same method.Is't possible?? I am getting error for the below program. It's my own coding, so how to do it correctly.

class Outer1
{
   public void amethod()
   {
      int i = 12;  
      class Inner1
      {
          public void bmethod()
          { 
             System.out.println(i);
          }
      }
   }
 
   public static void main(String args[])
   {
       Outer1 out = new Outer1();
       Outer1.Inner1 in = new Outer1().Inner1();
       in.bmethod();
    }
}    
   

[Norm Radder]

Could you copy and post the error message you get? That would make it faster.

[Joel McNary]

You can do this -- but the JLS says that those methods that you access must be final.

H:\user\Outer1.java:10: local variable i is accessed from within inner class; needs to be declared final
             System.out.println(i);
 
H:\user\Outer1.java:18: cannot find symbol
symbol  : class Inner1
location: class Outer1
       Outer1.Inner1 in = new Outer1().Inner1();
             ^
H:\user\Outer1.java:18: cannot find symbol
symbol  : method Inner1()
location: class Outer1
       Outer1.Inner1 in = new Outer1().Inner1();
                          ^

Problem is, your code still can't compile because Inner1 is not a member of the class Outer1 -- it's just a local class in your method. (I think it very odd that the compiler allows this, as I can't think of a useful reason for doing this.)

Remove the amethod() declaration and this should work:

public class Outer1
{
   int i = 12;
   class Inner1
   {
       public void bmethod()
       {
          System.out.println(i);
       }
   }
 
   public static void main(String args[])
   {
       Outer1 out = new Outer1();
       Outer1.Inner1 in = new Outer1.Inner1();
       in.bmethod();
    }
}

[Mark Henryson]

But I am still getting the error message as follows:

Coding I used:

public class Outer1
{
  int i = 12;  
  class Inner1
  {
    public void bmethod()
    { 
        System.out.println(i);
    }
  }
 
  public static void main(String args[])
  {
     Outer1 out = new Outer1();
     Outer1.Inner1 in = new Outer1().Inner1();
     in.bmethod();
  }
}

Outer1.java:17: cannot resolve symbol
symbol  : method Inner1  ()
location: class Outer1
       Outer1.Inner1 in = new Outer1().Inner1();
                          ^
1 error

[Joanne Neal]

Originally posted by Mark Henryson:

     Outer1.Inner1 in = new Outer1().Inner1();

That line should be

     Outer1.Inner1 in = new Outer1().new Inner1();

[Ulf Dittmer]

Joanne Neal wrote:

Outer1.Inner1 in = new Outer1().new Inner1();

I have never seen this notation - has that always been possible?
It's not exactly intuitive or reader-friendly, is it?

[Joanne Neal]

It does work.
I was just correcting the OP's code. I agree there are more reader friendly ways of writing it.

[Mark Henryson]

Hi,

Thanks for the reply Joanne Neal,Joel McNary and all.

I want the example coding for the below thing given in the code.
We didn't used the variable as final, but we are able to access it. Something I am missing??

 Can an inner class declared inside of a method access local variable of this method? 

[Arun Kumarr]

Any variable declared inside a method lives in the stack and has method scope.
Which means once the method is completed you can no longer access the variables.
So the declaration of "i" inside the method cannot be used by the class, as you might pass a reference of the class elsewhere and it cannot access the local variables.

But declaring the variable as final makes the variable a "compile-time constant" and hence they can be referenced outside.


class A{

//int i = 12; no compiler error
public void amethod()
{

int i = 12;

class Inner1
{

public void bmethod()
{
System.out.println(i);
}
}

}
}

[Ilja Preuss]

Originally posted by Ulf Dittmer:
I have never seen this notation - has that always been possible?

Since Java 1.1, which introduced inner classes, if I remember correctly.

It's not exactly intuitive or reader-friendly, is it?

What would be a better notation?

[Ilja Preuss]

Originally posted by Joel McNary:
a local class in your method. (I think it very odd that the compiler allows this, as I can't think of a useful reason for doing this.)

I use that feature for Visitor implementations that need to return (or rather collect) a value:

public IFoo getFooFor(IBaz baz) {
  class FooCollectingVisitor implement IBazVisitor {
    IFoo foo;
    public void visitBaz1(Baz1 baz) {
      foo = baz.getSpecialBaz1Foo();
    }
    ...
  }
  FooCollectingVisitor visitor = new FooCollectingVisitor();
  baz.accept(visitor);
  return visitor.foo;
}

Works well for me...