Java Array Initialization

[Kiran Sonaje]

I am getting lot compilation errors while compiling the program below.

public class LoadData 
{
    public static void main(String args[]) 
   {
      float invt[][];
      float []prct, grts[];
      float [][] sms ,  hms[];
 
      // invt = hms;  
      //hms=prct;
      // invt = grts;
      // grts = new float[1];  
      //hms = new float[2][5];  
    }
}

The errors are occuring on all the lines commented in the above code.
I'm specifically interested to know why the line "hms = new float[2][5];" fails in compilation.
Can anybody please explain this to me?

[Paul Sturrock]

Not an advanced question. Moving...

[Joanne Neal]

You always need to be careful when declaring several arrays on one line.
The line

float [][] sms ,  hms[];

is actually decalring a two dimensional array of floats and a one dimensional array of floats. It is equivalent to

float [][] sms;
float hms[];

Declare all your arrays on separate lines and then it should be more clear.

[Kiran Sonaje]

Hi Joanne,

Thanks for the reply.

For the above java code I am getting following compilation error

LoadData.java:13: incompatible types
found   : float[][]
required: float[][][]
                hms = new float[2][5];
                      ^
1 error

As per your suggetion if it is one dimensional array how does compiler complaining about 3 dimensional array. What you explained is solution for compilation and i am expecting what is the root cause for this? How JVM is handing this mechanism.

Waiting for reply .

Thanks

Kiran

[Joanne Neal]

My mistake.

float [][] hms[]

will declare a three dimensional array. So the reason for your compilation error is that you are trying to assign a two dimensional array to a three dimensional array reference.

[Kiran Sonaje]

Thanks Joanne

But this is not really i was expecting. I wanted why not how?

This is the answer, hope it will help you out.

Because hms is a three dimensional array.
This is what happens:
 
float[][]       sms,      hms[];
//    ^          ^         ^
//    |          |         |
//    |          |         +-- 'hms' is now a 1d array of 2d arrays (== 3d array!)
//    |          |
//    |          +-- 'sms' is now a 2d array
//    |
//    +-- declare some 2d arrays
 

 
So you need to instantiate hms like this:
 
hms = new float[2][][];
// or
hms = new float[2][2][];
// or
hms = new float[2][2][2];

Thanks

Kiran