not initialized

[Alberto Cancello]

At page 269 of Sierra&Bates' book SCJP for Java 5, there is a question:

1. class Zippy {
2. String[] x;
3. int[] a [] = {{1, 2}, {1}};
4. Object c = new long[4];
5. Object[] d = x;
6. }

The answer given as correct is "COmpilation succeeds" because all the array declarations are legal...
...but at line 5, x is not initialized, so the correct answer should be "Compilation fails due only to an error on line 5."

I try it with a compiler and it did not compile...

Bye,
Alberto

[Vlado Zajac]

Member variables are implicitly initialized (to zero, false or null), only local variables must be initialized explicitly.

[Sandeep Vaid]

Alberto,
Instance variables are initilized automatically.

[bnkiran kumar]

instance or static variables will be automaticaly initialized,in your example string array will be initialized with null which it is assiging to
object array,so no error will occur.

[Nilesh Deshpande]

There should be no error at compile time since the class instance object variables gets intialized to null. Take a look at the following code modified.
class Zippy {
String[] x;
int[] a [] = {{1, 2}, {1}};
Object c = new long[4];
Object[] d = x;
{
System.out.println(d);
}

public static void main(String arg[]){new Zippy();}
}

It gives you output==>null

[Alberto Cancello]

Ooops...
I put all inside a main() method.

Thank you.

Alberto

[Ravinder Singh]

Hi,

Pls. help me understand the following..I've customized the code a bit:

1. class Zippy {
2.String[] x;
3.int[] a [] = {{1, 2}, {1}};
4.Object c = new long[4];
 
5.Object[] d1 = x;
6.Object d2 = a;
7.Object [] d3 = a;
8.Object [][] d4 = a;
9. }

Line 6:
two dimension int array a assigned to an Object d2 --> code compiles

Line 7:
two dimension int array a assigned to a single dimension Object array d3 --> code compiles

Line 8:
two dimension int array a assigned to double dimension Object array d4 --> compiler error!

Q. Why does the code compiles with respect to line 6 and line 7 and NOT for line 8? What are the differences?

--------------
Ravinder

[Henry Wong]

Originally posted by Ravinder Singh:

Line 6:
two dimension int array a assigned to an Object d2 --> code compiles

Line 7:
two dimension int array a assigned to a single dimension Object array d3 --> code compiles

Line 8:
two dimension int array a assigned to double dimension Object array d4 --> compiler error!

Q. Why does the code compiles with respect to line 6 and line 7 and NOT for line 8? What are the differences?

The variable "a" is an array of array of ints.

Remember that an array is an object -- it inherits from object -- so...

- The variable "a" is also an object.

And this can also be further applied as...

- an array of ints is also an object.

hence...

- The variable "a" is also an array of objects.

And finally...

- The variable "a" is not an array of array of objects. It is an array of arrays of ints.

Henry

[Ravinder Singh]

Cool concept..
Thanks Henry!

-------------
Ravinder