for each

[jason roberts]

Can someone explain why the output to the following code is: 0 0 3 0

public class xyz
{
public static void main(String []args)
{
int []arr = {1,2,3,4};
 
for ( int i : arr )
{
   arr[i] = 0;
}
 
for ( int i : arr )
{
   System.out.println(i);
}
}
}

I would think there would be an ArrayOutOfBounds exception in the first for loop because it tries to set arr[4] = 0.

Thanks.

[sravani jetty]

Hi Jason,
In the first iteration i=1 which sets arr[1]=0 .The resulting array is {1,0,3,4}
In the second iteration i=0 which sets arr[0]=0. The resulting array is {0,0,3,4}
In the third iteration i=3 which sets arr[3]=0. The resulting array is {0,0,3,0}
In the last iteration i=0 which sets arr[0]=0. The resulting array is {0,0,3,0}

[jason roberts]

Hi Sravani,

In the first iteration i=1 which sets arr[1]=0 .The resulting array is {1,0,3,4}
In the second iteration i=0 which sets arr[0]=0. The resulting array is {0,0,3,4}
In the third iteration i=3 which sets arr[3]=0. The resulting array is {0,0,3,0}
In the last iteration i=0 which sets arr[0]=0. The resulting array is {0,0,3,0}

I guess I don't understand why it isn't:

In the first iteration i=1 which sets arr[1]=0 .The resulting array is {1,0,3,4}
In the second iteration i=2 which sets arr[2]=0. The resulting array is {1,0,0,4}
In the third iteration i=3 which sets arr[3]=0. The resulting array is {1,0,0,0}
In the last iteration i=4 which attempts to set arr[4]=0, and throws an exception.

I thought that since the array is {1,2,3,4}, the index values on each iteration would be 1,2,3 and 4.

Please help.

Thanks.

[jason roberts]

I think I get it now, the resulting array is used in the for-each loop, not just the initial array.

Thanks for your help.

[nitin pokhriyal]

can anybody explain why in iteration 2 i becomes 0 and in 4th iteration too also? how the value of i is changing. ?
[ June 27, 2007: Message edited by: nitin pokhriyal ]

[Ketul Shah]

can anybody explain why in iteration 2 i becomes 0 and in 4th iteration too also?

in the first iteration i initialized with arr[0] means i=1 so in the loop a[i=1]=0 which actually second element in the array.

same explanation for the third iteration.

I hope this gives you clear idea.

[nitin pokhriyal]

thanks buddy

[Manfred Klug]

Originally posted by jason roberts:
the resulting array is used in the for-each loop, not just the initial array.

There is no initial or resulting array. You have only one array. In your example the for loop is translated to something like this:

for (int cnt = 0; cnt < arr.length; ++cnt) {
    int i = arr[cnt];
    arr[i] = 0;
}