inner class

[leena rane]

I am not clear with inner classes terminology.
If we have class Outer
and it has inner class Inner,
then what do these imply from Inner?
(say var is a variable)
case 1:var is only defined in Outer
case 2:var is only defined in Outer as well as Inner

Outer.var
Outer.this.var
this.var
var

If Inner is defined as static/non-static how these work?
Thanx in advance

[ersin eser]

you are going to take the test on 29 th.
do you have Mr Khalid Mughal's book? it has an entire chapter and an excellent chart that summarizes the inner classes neatly.
You are going to need a good understanding of this topic and If you don't have the book and don't want to spend money tryhttp://www.javaranch.com/campfire/StoryInner.jsp
or if you have an access just goto local bookstore ( barnes & nobles ) grab a cup of coffee and preferably Khalid Mughal's book read the entire chapter & solve the practice questions.
Looks like you need a good review of this topic I would not ignore this chapter and last few days of your studies . you won't regret it.
ersin
[This message has been edited by ersin eser (edited October 22, 2001).]

[leena rane]

Thanx Ersin for the advise,
I do not hav Mughal,
only RHE,exam cram.
Can you answer my question?
(BTW if there is a javarancher from Mumbai who can give me the book for 1 day or 15 min-to xerox this chap, please mail me at [e-mail])

[Gagan Indus]

Okay lets talk about following case first :
class Outer {
int var ; //line#1
class Inner {
int var ; //line#2
void method ()
{
// here
}
}
}
var at line#2 shadows da var at line#1 .
So if we have to refer to var at line#2 , a special syntax of da form :
Outer.this.var
has to be used .

Now letc wot those 4 variable-access means if placed at line marked //here :
1) Outer.var : A'int valid . Only valid in case in which var at line#1 is declared static .
2) Outer.this.var : For every Inner class instance , there is one Outer class instance associated wid it.This access refers to tht Outer Instance's var , var declared at line#1 dat is .
3) this.var : Refer's to var at line#2 , i guess it is simple rite.
4) var : Same as 3rd , refers to var at line#2

Now comes da second case , when Inner class is declared "static"
In this case NO instace of outer class is associated wid any Instance of Inner class . And Inner class can ONLY refer to static variable of Outer class.
class Outer {
int var ; //line#1
static class Inner {
int var ; //line#2
void method ()
{
// here
}
}
}

1) Outer.var : A'int valid . Only valid in case in which var at line#1 is declared static .
2) Outer.this.var : NOT a valid syntax in this case
3) this.var : Refer's to var at line#2
4) var : Same as 3rd , refers to var at line#2

I hope , by now u understand , y da following code prints :
10
20
20
in dat order :

class Outer {
int var=10 ;     //line#1
static class Inner {
int var=20 ;     //line#2
void method ()
{
System.out.println (Outer.this.var );
System.out.println (this.var );
System.out.println (var);
//System.out.println (Outer.var );  // Is not valid u knw 
}
}
public static void main(String args[])
{
Outer o = new Outer();
Inner i = o.new Inner();
i.method();
}
}

Well i have to agree wid Ersin , Khalid's Inner class chapter is good
But even if u r not able to get hold of it , no regrets
Just have a look at Inner class chart , in velmurgan's notes . And understand everything it has to offer.
Hope someone from mumbai be able to help u out . Do lemme knw if i culd be of help.
Good luck for exam


------------------
Gagan (/^_^\) SCJP2
Die-hard JavaMonk -- little Java a day , keeps u going .

[Anonymous]

Gagan...
There is an error in the code you have posted.

<font face = courier new size = 3>
class Outer {int var=10 ;     //line#1
  static class Inner {
    int var=20 ;     //line#2
    void method (){
    System.out.println (Outer.this.var ); // *A*
    System.out.println (this.var );
    System.out.println (var);
    //System.out.println (Outer.var );  // Is not valid u knw
    }
  }
  public static void main(String args[]){
  Outer o = new Outer();
  Inner i = o.new Inner();
  i.method();
  }
}
</font>

There is an error in Line A.
This will not compile as top level nested classes cannot access non-static members of the enclosing class.
[This message has been edited by Shyamsundar Gururaj (edited October 23, 2001).]

[Anonymous]

Hi folks...
I have been studying Inner Classes from Khalid Mughal's book. Here are a few points that I had summarized for my notes...

1.Top-Level Nested Class (Static)
Declaration Context: As a static class member
What accessibility can be specified for Class/Interface? ALL
Is an outer instance present? NO
What is directly accessible in the enclosing context from within the class? Static members in the enclosing class.
Can the class define Static or Non-Static members or both? BOTH
2.Non-Static Inner Class
Declaration Context: As a non-static class member
What accessibility can be specified for Class/Interface? ALL
Is an outer instance present? YES
What is directly accessible in the enclosing context from within the class? ALL members in the enclosing class.
Can the class define Static or Non-Static members or both? ONLY Non-Static
3.Local Class (Static)
Declaration Context: In block with a static context
What accessibility can be specified for Class/Interface?NONE
Is an outer instance present? NO
What is directly accessible in the enclosing context from within the class? Static members in the enclosing class + local final variables
Can the class define Static or Non-Static members or both? ONLY non-static
4.Local Class (Non-Static)
Declaration Context: In block with a non-static context
What accessibility can be specified for Class/Interface? NONE
Is an outer instance present? YES
What is directly accessible in the enclosing context from within the class? ALL members in the enclosing class + Local final variables.
Can the class define Static or Non-Static members or both? ONLY non-static
5.Anonymous Class (Static)
Declaration Context: As an expression in a static context
What accessibility can be specified for Class/Interface? NONE
Is an outer instance present? NO
What is directly accessible in the enclosing context from within the class? Static members in the enclosing class + Local final variables.
Can the class define Static or Non-Static members or both? ONLY non-static
6.Anonymous Class (Non-Static)
Declaration Context: As an expression in a non-static context
What accessibility can be specified for Class/Interface? NONE
Is an outer instance present? YES
What is directly accessible in the enclosing context from within the class? ALL members in the enclosing class + Local final variables.
Can the class define Static or Non-Static members or both? ONLY non-static
7.Interface
Declaration Context: As a package member or a static class member
What accessibility can be specified for Class/Interface? PUBLIC ONLY
Is an outer instance present? N/A
What is directly accessible in the enclosing context from within the class? N/A
Can the class define Static or Non-Static members or both? Static variables + non-static method prototypes.

Hope this helps
Shyam
[This message has been edited by Shyamsundar Gururaj (edited October 23, 2001).]

[leena rane]

Thanx Gagan,
Thanx Shyamsundar

[Gagan Indus]

Oh yes Shyamsundar
dat static must be hangover of some ol' program
Sorry , the code i intentded to post was :

class Outer {
int var=10 ;     //line#1
 class Inner {
int var=20 ;     //line#2
void method ()
{
System.out.println (Outer.this.var );
System.out.println (this.var );
System.out.println (var);
//System.out.println (Outer.var );  // Is not valid u knw 
}
}
public static void main(String args[])
{
Outer o = new Outer();
Inner i = o.new Inner();
i.method();
}
}

------------------
Gagan (/^_^\) SCJP2
Die-hard JavaMonk -- little Java a day , keeps u going .