for Loop with y++ etc...

[zhewen]

haiy all, it is not easy, please answer in step, i know the result. thanks! zhewen

public class LabelTest {
public static void main(String[] args){
int j=3;
int y=0;
mainLoop: for(int i=0; i<j; i++){<br /> if (i>1) continue mainLoop;
y++;}
mainLoop: for(int=0; i<y; i++){>
y--;}
System.out.println(y);}}

[Madhav Lakkapragada]

zhewen:
Allow me in saying yout post is not very user friendly...
Original code should be:

public class LabelTest {
  public static void main(String[] args){
    int j=3;
    int y=0;
    mainLoop: for(int i= 0; i < j; i++){
    if (i>1) continue mainLoop;
      y++;}
    mainLoop: for(int i = 0; i < y; i++){
      y--;}
    System.out.println(y);}}

The main point to be learnt from this code is that the
second mainLoop label will override the first label.
Thats my understanding.
I waited till now to see if anyone will participate...since
no one has participated, I did some work on your code and here
is a modified version to see how the control flows.

public class LabelTest {
  public static void main(String[] args){
    int j=3;
    int y=0;
    
    mainLoop: for(int i = 0; i < j; i++){
    if (i>1) {
      System.out.println("Step Two");
      continue mainLoop;
      }
    
   System.out.println("Step One");
   y++;
   }
    
   mainLoop: for(int i = 0; i < y; i++){
      System.out.println("Step Three");
      y--;
   }
   
   System.out.println("Step Four");
   System.out.println(y);
  }
}

Regds.
- satya

[This message has been edited by Madhav Lakkapragada (edited June 20, 2000).]

[Anonymous]

Originally posted by Madhav Lakkapragada:
zhewen:
[...]
The main point to be learnt from this code is that the
second mainLoop label will override the first label.
Thats my understanding.
[...]

i am not exactly clear on what this code is supposed to exemplify.
could you please elaborate on it? what do you mean by "override.

[zhewen]

haiy satya, thanks for check. it is somewhat curiusly with the editor. wenn i now klick the symble editor, the code is ok. but in the post page just missing some code. to the programm, i think it is allowed with the same label, it is not overriding etc...,
anyone can help us further?
zhewen

[Madhav Lakkapragada]

overriding not in the sense of method overriding or
stuff like that, but say overwrites the previous label...
is that ok?
michal:
Please observe that in the above code, there are two mainLoop
labels. The JVM transfers the control to the next mainLoop
it finds after the current loop. Note that it doesnot
get confused by the presence of more than one labels with the
same name. (Not sure of the practical importance of this,
zhewen might want to comment why (s)he wrote this code )
Some more code:

public class LabelTest {
  public static void main(String[] args){
    int j = 3;
    int y = 0;
     
    mainLoop: for(int i = 0; i < j; i++){
    if (i > 1) {
      System.out.println("Step Two");
      continue mainLoop;
      }
    
   System.out.println("Step One");
   y++;
   }
    
   mainLoop: for(int z = 0; z < 1; z++)
               System.out.println("Step Four");
   System.out.println(y);
   
   mainLoop: for(int i = 0; i < y; i++){
      System.out.println("Step Three");
      y--;
   }   
  }
}

Hope I am clear now!
Regds.
- satya

[This message has been edited by Madhav Lakkapragada (edited June 20, 2000).]

[zhewen]

i think the two Loops will be excuted one after another, the result will be printed. i don't run the programm to see the result. wenn i skizz the route, i get the wrong result?
zhewen
thanks

[Anonymous]

Originally posted by Madhav Lakkapragada:
[b]overriding
Please observe that in the above code, there are two mainLoop
labels. The JVM transfers the control to the next mainLoop
it finds after the current loop. Note that it doesnot
get confused by the presence of more than one labels with the
same name. (Not sure of the practical importance of this,
zhewen might want to comment why (s)he wrote this code )
[/B]

Madhav:
so i guess what you are trying to say is that
labels in Java should be unique in the loop scope?
thanks,
PS
i just thought i was missing something here.

[Madhav Lakkapragada]

so i guess what you are trying to say is that
labels in Java should be unique in the loop scope?
I don't think so...In the above examples, the labels are
not unique, IMO. What I understood was that the JVM
continues execution at the label given after the continue
stmt. However, if this label is declared (multiple number
of times) after the loop, it continues from the next
location where it finds the label. More elaborately:

Line 1: MyLabel: //Loop statements
     2      {
     3   //some code
     4   continue MyLabel;
     5   }

Will continue from Line 1, till the loop terminating
condition is reached.

Line 1: MyLabel: //Loop statements
     2      {
     3   //some code
     4   continue MyLabel;
     5   }
     6
     7  MyLabel: //Some other code

This will continue from line 7 (not at line 1).

Line 1: MyLabel: //Loop statements
     2      {
     3   //some code
     4   continue MyLabel;
     5   }
     6
     7  MyLabel: //Some other code
     8  //Add more code
     9  MyLabel: //Add more and more code

This will also continue from line 7 (not at line 1
and not line 9). Code at line 7 is executed and then
the execution will continue on.
Hope its clear now!
Regds.
- satya

[Jim Yingst]

I'd say that yes, the labels should be unique within their scopes, in the sense that this is good programming practice to avoid confusion. However it appears that this is not a requirement of Java, to my surprise.

[Shiny]

Satya
I see you are logging now, as Madhav [renameTo("Madhav")] !?
Well, I don't seem to get the behaviour (of the code) as you have explained above. I think, in a given scope, till the leading condition is satisfied, the 'continue label' does NOT move the flow forward in the code to next statement where 'label' is reused. Try this code:
public class Test {
public static void main(String args[]) {
int j=4;
int y=0;
mainLoop: for(int i = 0; i < j; i++){
if (i==2) {
System.out.println("Step Two");
continue mainLoop;
}
System.out.println("Step One");
y++;
}
mainLoop: for(int i = 0; i < y; i++){
System.out.println("Step Three");
y--; }
System.out.println("Step Four");
System.out.println(y);
}
}
The output on my machine says:
Step One
Step One
Step Two
Step One
Step Three
Step Three
Step Four
1
instead of (if your logic was true):
Step One
Step One
Step Two
Step Three
Step Three
Step Four
'whatever y evaluates to'
correct me if I am mistaken,
by the way, I am taking the exam tomorrow - wish me luck !

[Michal Harezlak]

satya:
I thing I have gotten your point now.
I am afraid you might be mistaken.
1. a statement cannot be labeled with the same identifier
as one of its enclosing statement. (it is allowed to
reuse label later)

...
 loop: while (true)
  loop: while (true);
...

will not compile.
while this one will

...
 loop: while (false);
 loop: while (true);
...

2. continue statement will not jump out of
enclosing loop even if the label is reuse later.

...
 loop: while(i>10){
  i++;
  continue loop; 
 }
 loop: while (true);
...

continue loop will jump to the beginning of the enclosing loop.
regards, michal.

[Michal Harezlak]

Originally posted by Madhav Lakkapragada:
[B]
so i guess what you are trying to say is that
labels in Java should be unique in the loop scope?
I don't think so...In the above examples, the labels are
not unique, IMO. What I understood was that the JVM
continues execution at the label given after the continue
stmt. However, if this label is declared (multiple number
of times) after the loop, it continues from the next
location where it finds the label. More elaborately:

Line 1: MyLabel: //Loop statements
     2      {
     3   //some code
     4   continue MyLabel;
     5   }

Will continue from Line 1, till the loop terminating
condition is reached.

Line 1: MyLabel: //Loop statements
     2      {
     3   //some code
     4   continue MyLabel;
     5   }
     6
     7  MyLabel: //Some other code

This will continue from line 7 (not at line 1).

Line 1: MyLabel: //Loop statements
     2      {
     3   //some code
     4   continue MyLabel;
     5   }
     6
     7  MyLabel: //Some other code
     8  //Add more code
     9  MyLabel: //Add more and more code

This will also continue from line 7 (not at line 1
and not line 9). Code at line 7 is executed and then
the execution will continue on.
Hope its clear now!
Regds.
- satya
[/B]

I am afraid you might be mistaken.
1. a statement cannot be labeled with the same identifier
as one of its enclosing statement. (it is allowed to
reuse label later)

...
 loop: while (true)
  loop: while (true);
...

will not compile.
while this one will

...
 loop: while (false);
 loop: while (true);
...

2. continue statement will not jump out of
enclosing loop even if the label is reuse later.

...
 loop: while(i>10){
  i++;
  continue loop; 
 }
 loop: while (true);
...

continue loop will jump to the beginning of the enclosing loop.
regards, michal.

[Madhav Lakkapragada]

Originally posted by Shiny:
Satya
I see you are logging now, as Madhav [renameTo("Madhav")] !"> /i]
yup, the bartender stuff needs a first_name last_name kinda...
[i]instead of (if your logic was true):
Step One
Step One
Step Two
Step Three
Step Three
Step Four
'whatever y evaluates to'
correct me if I am mistaken,
yes, indeed you are correct. When I posted the code, I forgot
to verify the for loop really terminates and thats the reason
why we goto the next mailLoop label and not b'coz of what I said
earlier...Thanks for correcting.
by the way, I am taking the exam tomorrow - wish me luck
best wishes...may be you are already done with your exam !
michal:
i stand corrected, please see above.
Regds.
- satya