question regarding initialzer.

[sura watthana]

Hi,
Looking at the code below, I don't understand why the statement at (5) is valid since variable 'height' has not been declared before it is initialized?
could somebody help me out? Thanks

 
class NonStaticInitializers {
    int length  = 10;                   // (1)
//  double area = length * width;       // (2) Not Ok. Illegal forward reference.
    double area = length * this.width;  // (3) Ok, but width has default value 0.
    int width   = 10;                   // (4)
 
    int sqSide = height = 20;           // (5) OK. Legal forward reference.
    int height;                         // (6)
}
 
 :)  
 

[Barry Gaunt]

You may find that this earlier thread helps you.

[navneet shrivastava]

interesting question.
i guess for this we need to know how JVM/compiler behaves.
waiting for experts excerpts.

navneet

[marc weber]

Actually, I do get an illegal forward reference error with the above code, as I do with the following...

public class Forward{
   int a = b = 20; //error here...
   int b;
 
   void values(){
      System.out.println("a is " + a + ", and b is " + b);
   }
 
   public static void main(String[] args){
      Forward f = new Forward();
      f.values();
   }
}

(I'm running 1.3 at work. Might that be the difference?)
[ September 20, 2004: Message edited by: marc weber ]

[Inuka Vincit]

public class Forward{
   int a = b = 20;
   int b;
 
   void values(){
      System.out.println("a is " + a + ", and b is " + b);
   }
 
   public static void main(String[] args){
      Forward f = new Forward();
      f.values();
   }
}

(I'm running 1.3 at work. Might that be the difference?)

[ September 20, 2004: Message edited by: marc weber ][/qb]<hr></blockquote>



exact same code works for me it should
here is an other good example from the java language spec

[B]

class UseBeforeDeclaration {
static {
x = 100; // ok - assignment
int y = x + 1; // error - read before declaration
int v = x = 3; // ok - x at left hand side of assignment
int z = UseBeforeDeclaration.x * 2;
// ok - not accessed via simple name
Object o = new Object(){ 
void foo(){x++;} // ok - occurs in a different class
{x++;} // ok - occurs in a different class
    };
  }
{
j = 200; // ok - assignment
j = j + 1; // error - right hand side reads before declaration
int k = j = j + 1; 
int n = j = 300; // ok - j at left hand side of assignment
int h = j++; // error - read before declaration
int l = this.j * 3; // ok - not accessed via simple name
Object o = new Object(){ 
void foo(){j++;} // ok - occurs in a different class
{ j = j + 1;} // ok - occurs in a different class
};
}
int w = x= 3; // ok - x at left hand side of assignment
int p = x; // ok - instance initializers may access static fields
static int u = (new Object(){int bar(){return x;}}).bar();
// ok - occurs in a different class
static int x;
int m = j = 4; // ok - j at left hand side of assignment
int o = (new Object(){int bar(){return j;}}).bar(); 
// ok - occurs in a different class
int j;
}

[/B]
web page

[ September 20, 2004: Message edited by: Inuka Vincit ]
[ September 20, 2004: Message edited by: Inuka Vincit ]

[marc weber]

Originally posted by Inuka Vincit:
exact same code works for me it should

Interesting... I'll have to check this using 1.4 when I get home.

[marc weber]

Update: Both pieces of code work with 1.4, but neither worked with 1.3.

Note: The UseBeforeDeclaration class above is from the Second Edition of the JLS (section 8.3.2.3). I couldn't find anything to parallel it in the First Edition.

JLS, 2nd Ed., Sect. 8.3.2.3: http://java.sun.com/docs/books/jls/second_edition/html/classes.doc.html#287406
[ September 20, 2004: Message edited by: marc weber ]

[Inuka Vincit]

Originally posted by marc weber:
Update: Both pieces of code work with 1.4, but neither worked with 1.3.

Note: The UseBeforeDeclaration class above is from the Second Edition of the JLS (section 8.3.2.3). I couldn't find anything to parallel it in the First Edition.

JLS, 2nd Ed., Sect. 8.3.2.3: http://java.sun.com/docs/books/jls/second_edition/html/classes.doc.html#287406

[ September 20, 2004: Message edited by: marc weber ]

baah hate when that sort of thing happened, end up confusing your self

[marc weber]

Well, I definitely learned something. Thanks for the example!

What's instructive to me is the way they phrase the comments in the JLS code: "//error - read before declaration." Technically, I suppose it's all the same, but the problem of trying to "read" a variable before it's declared makes more sense to me than discerning "left/right" in something like "int a = b = 20."
[ September 21, 2004: Message edited by: marc weber ]

[PNS Subramanian]

This is the message i get for the code below
C:\Data\bea8.1\jdk141_03\bin\Test2.java:6: cannot resolve symbol
symbol : variable j
location: class Test2
int i = j = 20;
^
1 error

Process completed with exit code 1

import java.io.*;
public class Test2 {
    private static PrintStream log = System.out;
    public static void main(String a[]) {
        log.println("Inside main");
        int i = j = 20;
    }
}

Does this have anything to do with the version being used ?

[Purushoth Thambu]

I guess you overlooked declaring j. The code you posted doesn't contain declaration for j hence the error.

declare the variable j before you use. Since j is local variable you cannot have forward referencing.

[Nandish KB]

Hey I checked the same code with Eclipse.Its giving compiler error.
Even I tried with

int a=b=3;
static int b; // this also gives me error, I think it should work rt ?. as forward referncing for static vars is allowed


int a = b = 4;
int b; // here also its giving errr

plz clarify my doubt

Thanx
Nandish

[Nandish KB]

Ohhhhhhhhhh sorrrrrrrry,
I actually written those codes in main() method.
Sorry to post wrong Qn ! :-(
Regards,
Nandish