Array assignment doubt

[Satish Kota]

How come this compiles

String[][] s=null;
Object[] o=s;

Even though it compiles why doesnt it generate runtime error as o and s are of different dimension.

[Henry Wong]

Originally posted by Satish Kota:
How come this compiles

String[][] s=null;
Object[] o=s;

Even though it compiles why doesnt it generate runtime error as o and s are of different dimension.

It compiles and runs fine because it is valid... basically...

"s" is an array of an array of strings. Since arrays are also objects, an "array of strings" is also an object. Hence, "s" is also an array of objects.

Henry

[Satish Kota]

This is what makes it more confusing

class Animal { }
class Dog extends Animal { }

Dog[][] d=new Dog[9][];
Object o=d; //Compiles
Object[] o1=d; //Compiles
Object[][] o2=d; //Compiles, SAY THIS IS LINE 6
Object[][][] o3=d; //Doesnt Compile

Animal a=d; //Doesnt Compile
Animal[] a1=d; //Doesnt Compile
Animal[][] a2=d; // Compiles
Animal[][][] a3=d; //Doesnt Compile


Dog[] d=new Dog[9];
Object o=d; //Compiles
Object[] o1=d; //Compiles

Animal a1=d; //Doesnt Compile
Animal[] a2=d; //Compiles

int[][] i=new int[9][]; //Compiles
Object o=i; //Compiles
Object[] o1=i; //Compiles
Object[][] o2=i; // Doesnt Compile, SAY THIS IS LINE 22

int[] i=new int[9]; //Compiles
Object o=i; //Compiles
Object[] o1=i; // Doesnt Compile, SAY THIS IS LINE 26


When Line 6 compiles why are Line 22,26 generating error. In both cases the indexes are same. Then why is this error coming ?
[ November 27, 2006: Message edited by: Satish Kota ]

[Andy Morris]

You've misread/misinterpretted Henry's response.

It's not that the type of object you're storing in your array is of type Object, it's the fact that arrays themselves are objects.

Therefore:
* A String array can be assigned to an object
* An array of String arrays (and using the principle above) can be assigned to an array of objects (your String arrays are an array of objects).

If you understand that then you'll understand why you can't assign an array of String arrays to a 3d object array - or anything else with that many dimensions.