I'm so confused, pls help

[Jim Yeung]

Hi, all,
I got a question as follows:
=================================
class x{
y b=new y();
x(){
Sytem.out.print("x");
}
}

class y{
y(){
System.out.print("y");
}
}

public class z extends x{
y y0=new y();
z(){
System.out.print("z");
}
public static void main(String[] args){
new z();
}
}

The result is yxyz, I'm very confused, as my understanding, it should be yxz, how come? pls help me, thanks a lot!

[Joe San]

Hi Above,

The answer is quite obvious in your code. Didnt you see that you are calling the the class y constructor twice?? Hence the result YXYZ. See the comments in the code below.

Your code,

class x{
y b=new y(); //Line 1. Go to Line 2.
x(){// Line 3. X gets printed here and goes to Line 4. O/P = YX
Sytem.out.print("x");
}
}
 
class y{
y(){ //Line 2
System.out.print("y"); //Y is printed first and then go to Line 3
}
}
 
public class z extends x{//Line 4 z class gets loaded. goto Line 5
y y0=new y();// Line 5. Again call y's constructor. o/P here = YXY
z(){ //[B]Line 6. o/P here = YXYZ[/B]
System.out.print("z");
}
public static void main(String[] args){
new z(); //call the superclass constructor. go to line 1
}
}

Try changing in the class z as below and tell me what the O/P will be?

public class z extends x{

z(){
System.out.print("z");
}
y y0=new y();
public static void main(String[] args){
new z();
}
}

What will be the O/P in tha above case?? YXZY. did you get it??

Regards.
Jothi Shankar Kumar. S
[ November 03, 2006: Message edited by: Jothi Shankar Kumar Sankararaj ]

[Jim Yeung]

Originally posted by Jothi Shankar Kumar Sankararaj:
Hi Above,

The answer is quite obvious in your code. Didnt you see that you are calling the the class y constructor twice?? Hence the result YXYZ. See the comments in the code below.

Your code,

class x{
y b=new y(); //Line 1. Go to Line 2.
x(){// Line 3. X gets printed here and goes to Line 4. O/P = YX
Sytem.out.print("x");
}
}
 
class y{
y(){ //Line 2
System.out.print("y"); //Y is printed first and then go to Line 3
}
}
 
public class z extends x{//Line 4 z class gets loaded. goto Line 5
y y0=new y();// Line 5. Again call y's constructor. o/P here = YXY
z(){ //[B]Line 6. o/P here = YXYZ[/B]
System.out.print("z");
}
public static void main(String[] args){
new z(); //call the superclass constructor. go to line 1
}
}

Try changing in the class z as below and tell me what the O/P will be?

public class z extends x{

z(){
System.out.print("z");
}
y y0=new y();
public static void main(String[] args){
new z();
}
}

What will be the O/P in tha above case?? YXZY. did you get it??

Regards.
Jothi Shankar Kumar. S

[ November 03, 2006: Message edited by: Jothi Shankar Kumar Sankararaj ]

Hi, Jothi, thanks for your response, if you don't mind my stupidity, is it true the program has to first execute x's other objects located before x's constructor when calling x's constructor ?

[Joe San]

Hi "I Dont know you name",

In real life the rule is parent must exist before the child can. In OO terms this means parent class must exist before the child class can. So whenever you call the child class constructor, there is an implicit call to it's parent constructor. Never forget this.

The program runs sequentially, so any code in a contructor is taken care in the order in which they are written.

Regards,
Jothi Shankar Kumar. S

[ November 04, 2006: Message edited by: Jothi Shankar Kumar Sankararaj ]
[ November 04, 2006: Message edited by: Jothi Shankar Kumar Sankararaj ]

[Jim Yeung]

Originally posted by Jothi Shankar Kumar Sankararaj:
Hi "I Dont know you name",

In real life the rule is parent must exist before the child can. In OO terms this means parent class must exist before the child class can. So whenever you call the child class constructor, there is an implicit call to it's parent constructor. Never forget this.

The program runs sequentially, so any code in a contructor is taken care in the order in which they are written.

Regards,
Jothi Shankar Kumar. S

[ November 04, 2006: Message edited by: Jothi Shankar Kumar Sankararaj ]

[ November 04, 2006: Message edited by: Jothi Shankar Kumar Sankararaj ]

Thanks a lot, Jothi, what confused me is y b=new y() is not within x's constructor, why does the code execute it before execute x's constructor?

[David O'Meara]

"crazy_geek",
Welcome to the JavaRanch.

We're a friendly group, but we do require members to have valid display names.

Display names must be two words: your first name, a space, then your last name. Fictitious names are not allowed.

Please edit your profile and correct your display name since accounts with display names get deleted, often without warning

thanks,
Dave

[Jim Yeung]

Originally posted by David O'Meara:
"crazy_geek",
Welcome to the JavaRanch.

We're a friendly group, but we do require members to have valid display names.

Display names must be two words: your first name, a space, then your last name. Fictitious names are not allowed.

Please edit your profile and correct your display name since accounts with display names get deleted, often without warning

thanks,
Dave

Hi, David,
I've changed my display name, but my topic still shows "crazy_geek", not worked, was I doing sth wrong?
:roll:

[Sanjeev Singh]

Hi Above,
Jothi answer are more than enough to gulp the basic concepts.

Thanks jothi