super class where?

[payal sharma]

class Test {
 int y=1;
 int a=6;  
 Test() {
   this(a);
 }
 Test(int x) {
   if ( x > y )
     a = y*6;
   else
     a = y*9;
     a++;
 System.out.println(a); 
 }  
 public static void main(String [] args) {
    Test t = new Test();
 }
}

C:\JAVA>javac Test.java
Test.java:7: Can't reference a before the superclass constructor has been
called.
this(a);
^
1 error
Why it is accessing for superclass constructor?
thanks in advance
payal
[This message has been edited by payal sharma (edited July 27, 2001).]

[Mikael Jonasson]

You are trying to use an instancevariable, but since the object isn't finnished constructing it doesn't really exist yet. Remember that all classes ultimatly extends Object, so there is always a call to the superclass. All a this()-call does is delay the call to Objects constructor.
/Mike

[Desai Sandeep]

Hi Payal,
Implicitly every class has its super class as java.lang.Object. Same is the case here.
When you try to instantiate class Test, the Constructor is called first and then the instance variables gets initialized.However calling this(a) means you are calling Constructor Test(int) when a is still not initialized, i.e the Object of Test is still not created and hence instance varaible a is still not initialized.
The above problem could be solved, if you modify the code to :

<font size=+0><pre>
class Test {
     int y=1;  // These statements are executed after the 
     int a=6;    // Test object is created
     Test() {
         this(10);
     }
     Test(int x) {
         super() // implicity called;after this call you can refer to instance variables  declared in Test!   
         if (x > y)
             a = y*6;
         else
             a = y*9;
         a++;
         System.out.println(a); 
     }  

     public static void main(String [] args) {
         Test t = new Test(10);
     }
}
</pre></font>

Hope this helps,
Sandeep
SCJP2, OCSD(Oracle JDeveloper), OCED(Oracle Internet Platform)
[This message has been edited by Desai Sandeep (edited July 28, 2001).]