Creation of Object Q

[Nitin Bhagwat]

Following code works fine. Question is how value of av is available before completion of constructor? (I think, class members - methods and variables (except static) are available only after completion of constructor). Please correct if i am wrong.

 
class a
{
  int av = am();
  {
     System.out.println("initializer "+av);
  }
 
  a()
  {
     System.out.println("constructor "+av);
  }
 
  int am()
  {
    System.out.println("method");
    return 1;
  }
 
}
class t
{
  public static void main(String pp[])
  {
    new a();
  }
}
 
 

[Corey McGlone]

Originally posted by Nitin Bhagwat:
I think, class members - methods and variables (except static) are available only after completion of constructor

Instance members are actually initialized prior to the constructor being executed so all instance members are available within the constructor.

[Manikandan Jayaraman]

Hi Nitin,
The concept is this. Consider a base class and derived class has static initialiser block and instance initialiser block. The order of execution is as follows :
===
STATIC Instance Initialiser - Base
STATIC Instance Initialiser - Derived
Instance Initialiser - Base
Parent cons. called
Instance Initialiser - Derived
Constructor of derived
===
Below is a code. Try that and you will get it.

 
class Parent
{
static int i1 = 5;
static int l1;
int j1 = 7;
int k1;
 
{ 
System.out.println("Before Instance Initialiser - Base");
System.out.println(i1 + "," + j1 + "," + k1 + "," + l1 );
j1 = 70; l1 = 20; 
System.out.println("After Instance Initialiser - Base");
System.out.println(i1 + "," + j1 + "," + k1 + "," + l1 );
} // Instance initializer block
 
static 
{
System.out.println("Before STATIC Instance Initialiser - Base");
System.out.println(i1 + "," + l1 );
i1 = 50; 
System.out.println("After STATIC Instance Initialiser - Base");
System.out.println(i1 + "," + l1 );

} // Static initializer block
 
public Parent() { System.out.println("Parent Basic cons. called");}
 
public Parent(int m) 
{
System.out.println("Parent Overloaded Cons. called");
System.out.println(i1 + "," + j1 + "," + k1 + "," + l1 + "," + m);
}
 
};
 
public class InstanceInitialiser extends Parent
{
static int i2 = 5;
static int l2;
int j2 = 7;
int k2;
 
{ 
System.out.println("Before Instance Initialiser - Derived");
System.out.println(i2 + "," + j2 + "," + k2 + "," + l2); 
j2 = 70; l2 = 20; 
System.out.println("After Instance Initialiser - Derived");
System.out.println(i2 + "," + j2 + "," + k2 + "," + l2);
} // Instance initializer block

static 
{
System.out.println("Before STATIC Instance Initialiser - Derived");
System.out.println(i2 + ","  + l2);
i2 = 50; 
System.out.println("After STATIC Instance Initialiser - Derived");
System.out.println(i2 + "," + l2);
 
} // Static initializer block
 
public InstanceInitialiser(int m) 
{
System.out.println("In Constructor of derived");
System.out.println(i2 + "," + j2 + "," + k2 + "," + l2 + "," + m);
}
 
public static void main(String[] args) 
{
InstanceInitialiser obj = new InstanceInitialiser(l2);
}
}

Cheers!
_Mani

[Nitin Bhagwat]

Thank you Mani, Excellent help!