Static Variables Compilation

[Hari Mohan]

Hi, please look at the code snippets below........

a.)

public class Test{
private int i = j;
private int j = 10;
public static void main(String args[]){
System.out.println((new Test()).i);
}
}

throws a compilation error

b.)

public class Test{
private int i = j;
private static int j = 10;
public static void main(String args[]){
System.out.println((new Test()).i);
}
}

compiles well and gives an output 10;

c.)

public class Test{
private static int i = j;
private static int j = 10;
public static void main(String args[]){
System.out.println((new Test()).i);
}
}

once again doesn't compile

d.)

public class Test{
private int i = giveMeJ();
private int j = 10;
private int giveMeJ(){
return j;
}
public static void main(String args[]){
System.out.println((new Test()).i);
}
}

compiles fine but gives an output 0 (???)

e.)

public class Test{
private int i = giveMeJ();
private static int j = 10;
private static int giveMeJ(){
return j;
}
public static void main(String args[]){
System.out.println((new Test()).i);
}
}

gives me 10

and finally
f)

public class Test{
private static int i = giveMeJ();
private static int j = 10;
private static int giveMeJ(){
return j;
}
public static void main(String args[]){
System.out.println((new Test()).i);
}
}

gives me 0;

Can somebody please explain me the reasons for codes working in the way shown?

[Ronald Schild]

A and C are trying to use j before it exists.

Consider the code:

 
  int j = 0 ; 
  for( ; i < j ; ++i ) {
   // ... do things
  }
 
  int i = 0 ; 

This doesn't work. The variable i must be declared and initialized before it is used. Instance variables are initialized to a default value, but you must declare them still.

B works, because here j is a static variable. This means that it is a class variable and is initialized when the class is initialized. This is before any object instantiation, and so before i exists.

D works. The variable j is declared and exists so it can be used in method giveMeJ(). At the point where it is called to assign i, j has not yet been set to the value 10, so the default value 0 is returned.

At E, j was initialized during class initialization. It works like D but now returns 10.

For F I think you can deduct the right answer based on D.

[Hari Mohan]

Thank you Ronald....The only confusion I had was with (d). But now, it's clear, and as you had explained, The code below

public class Test{
private int j = 10;
private int i = giveMeJ();
private int giveMeJ(){
return j;
}
public static void main(String args[]){
Test test=new Test();
System.out.println(test.i);
}
 
}

compiles and gives an output 10
because j has been initialized even before i was assigned with j returned by giveMeJ........That fits.....Thank you so much....

[Sagar Rohankar]

From Ronalds explanation can I deduce the initialization steps for a class like this :

1 -- > Class variables initialized by default value

2 -- > Instance variables initialized by default value

3 -- > Class Variables gets defined by there hard coded values.

4 -- > Instance Variables gets defined by there hard coded values.

Correct me If I am wrong !