Forward Referencing

[Satish Kota]

The following code gives forward reference error

public class test
{
static
{
  System.out.println(x);
}
static int x=23;
 
  public static void main(String[] args)
  {
  
  }
}

But when i replace System.out.println(x); in static block to assignment operation like x=33. The programe compiles fine.

public class test
{
 
static
{
  x=33;
}
 
static int x=23;
 
  public static void main(String[] args)
  {
  
  }
}

Why isnt forward referencing error getting applicable when we are assigning value to static variables?

[Rancy Chadha]

Hi Satish,

public class Test
{
static{
System.out.println(x);
}
static int x=23;

public static void main(String[] args) { }
}

The reason why this code gives you forward referencing error is because here you are trying to print value of x. Which is violating the rule of declaration before read.
For forward referencing to work you can using the variable as the destination but not as a source. What I mean is:

int y=0;
y = x = 5; //This expression evaluates as (y = (x = 5))
int x;
Above code will work fine because here x is used on left hand side as source for inner expression.
Where as same code will give error if you do

int y=0;
y=x; // x is used as source
int x;
In your code you were using x as source so you were getting the error.
I hope this clears the point.

Thanks,
Rancy

[raja kanak]

Originally posted by Satish Kota:
The following code gives forward reference error

public class test
{
static
{
  System.out.println(x);
}
static int x=23;
 
  public static void main(String[] args)
  {
  
  }
}

But when i replace System.out.println(x); in static block to assignment operation like x=33. The programe compiles fine.

public class test
{
 
static
{
  x=33;
}
 
static int x=23;
 
  public static void main(String[] args)
  {
  
  }
}

Why isnt forward referencing error getting applicable when we are assigning value to static variables?

which one will run first
static block or static declaration/initialization

[hardikjava shah]

static code runs in the order in which they appear in the code.

[Satish Kota]

Originally posted by Rancy Chadha:
For forward referencing to work you can using the variable as the destination but not as a source

I think that rule applies only to static block. In case of instance block i am able to forward reference a variable x using this pointer. As shown :

public class test
{
{
  System.out.println(this.x);
}
int x=23;
}

Any comments?