array question

[reubin haz]

Here is a question in array:

 
 
  1.  public class Test {
  2.     public static void main(String [] args) {
  3.     int [] [] [] x = new int [3] [] [];
  4.     int i,j;
  5.     x[0] = new int[4][];
  6.     x[1] = new int[2][];
  7.     x[2] = new int[5][];
  8.     for (i=0; i<x.length; i++)
  9.        for (j=0; j<x[i].length; j++) {
 10.           x[i][j] = new int [i + j + 1];
 11.           System.out.println("size = " + x[i][j].length);
 12.        }
 13.
     }
 14.  } 

How could the output is 11, not 9? I thought both x.length and x[i].length are 3. How would line 10 change the length?
Thanks.

[Geethakrishna Srihari]

1)The code output is not single line output.The output is:
size = 1
size = 2
size = 3
size = 4
size = 2
size = 3
size = 3
size = 4
size = 5
size = 6
size = 7

2)Length of x and x[i] are not same
length of x = 3

length of x[0]=4,x[1]=2,x[2]=5

3)Line 3 changes the length ; it allocates objects.If that line is not used we wud get null pointer exception.

My Doubt:
If the code were like:
public class Test
{
public static void main(String [] args)
{
int [] [] [] x = new int [3] [] [];
int i,j;
x[0] = new int[4][];
x[1] = new int[2][];
x[2] = new int[5][];
for (i=0; i<x.length; i++)
for (j=0; j<x[i].length; j++)
x[i][j] = new int [i + j + 1];
System.out.println("size = " + x[i][j].length);
}
}
I get the compiler error that i and j not initialized....
How come thats possible?
I and j wud have surely initialized in the for loop?

[Vlado Zajac]

the compiler doesn't know that the outer loop body (the inner loop) executes so j (used in the println statement) may not be initialized. (The println statement is outside of both loops.)

[reubin haz]

Can someone explain more detail about this compiler problem? Thanks.
[ May 26, 2005: Message edited by: reubin nibuer ]

[Allain Walker]

I think that taking out the curly braces has reduced the scope of the loops, I believe that the scope has been reduced it to 1 line , as in an if statement.
at best I think the compiler sees this;

for (i=0; i<x.length; i++)
{
  for (j=0; j<x[i].length; j++)
  {
    x[i][j] = new int [i + j + 1];
  }
}
System.out.println("size = " + x[i][j].length);

At worst it would see this;

  
for (i=0; i<x.length; i++)
{
}
for (j=0; j<x[i].length; j++)
{
}
x[i][j] = new int [i + j + 1];
System.out.println("size = " + x[i][j].length);

At any rate you do't save anything by cutting out the braces the compiler puts them in for you.
R1885

[Geethakrishna Srihari]

No...the compiler problem refers to the code which i pasted.

[Allain Walker]

Sorry thought that it was the other code.

[Allain Walker]

What is happening is that you are creating a new array of int that has i+j+1 members.
So when you return th esize of the last array by calling x[i][j].length it returns the number of members of the new int array.
try putting this in

 
public class Test {
public static void main(String [] args) {
int [] [] [] x = new int [3] [] [];
int i,j;
x[0] = new int[4][];
x[1] = new int[2][];
x[2] = new int[5][];
for (i=0; i<x.length; i++)
for (j=0; j<x[i].length; j++) {
int a[]= {(i + j + 1)};
x[i][j] = a;
System.out.println("int = "+ (i + j + 1));
System.out.println("size = " + x[i][j].length);
System.out.println("member value = " + x[i][j][0]);
System.out.println("\\\\\\\\\\\\\\\\\\\\\\");
}
}
}

and you will see the difference in the outputs.
Hope it helps