Clone

[Jay Kay]

class CloneTest
{
public static void main(String[] args)
{
int ia[ ][ ] = { { 1 , 2}, null };
int ja[ ][ ] = (int[ ] [ ])ia.clone();
System.out.print((ia == ja) + " ");
System.out.println(ia[0] == ja[0] && ia[1] == ja[1]);
}
}
What is the difference between ia and ja
Any help is greatly appreciated.
-Jay

[Ragu Sivaraman]

Arrays are Objects in java
Here a shallow cloning is happening
ia and ja becomes two different arrays of array references
Thats why ia==ja becomes false and
ia[1] == ja[1] becomes true
Ragu
[This message has been edited by Ragu Sivaraman (edited September 23, 2001).]

[Sasikanth Malladi]

How come that
int ia[ ][ ] = { { 1 , 2}, null };
is accepted by the compiler when null can't be cast or promoted to an int?
Shashi

[Valentin Crettaz]

since this is a bidimensionnal array of int, null stands here for the reference to the second array so this is allowed as far as I know. But I think that the following declaration would not be accepted by the compiler
int[][] array = {{1,2},{1,null}};
Val

[Jay Kay]

Here a shallow cloning is happening
ia and ja becomes two different arrays of array references
Thats why ia==ja becomes false and
ia[1] == ja[1] becomes true
Ragu
Thanks Ragu.
Some follow up questions,
1. What is Shallow Cloning
int ia[ ][ ] = { { 1 , 2}, null };
int ja[ ][ ] = (int[ ] [ ])ia.clone();
2. How is ia[1] (which is null) = ja[1] (which is null) as two nulls cannot be equal
3. is ia[0][0]=ja[0][0] (is it 1) and
ia[0][1]=ja[0][1] (is it 2)

[james hoskins]

hello jay,
shallow cloning is when you simply call the clone() method on an object which produces an exact copy of that object.
deep cloning happens when the object you call is an aggregate object which implements the Cloneable interface. this interface is a marker interface which tells you that when you call clone() on this aggregate object, it will recursively clone all the objects it contains references to.
kind regards,
james

[Jane Griscti]

Hi guys,
The Object.clone() method does a 'shallow copy'. It will copy all the fields of the cloned object; but if any of them are reference fields (non-primitive type variables) then only a copy of the reference is made. It will not create and copy the objects referenced..
For example, if a class has a field <code>Object myObject</code> the clone will reference the same 'myObject'. Any changes made to the cloned 'myObject' will be seen in the original 'myObject'.
If you want entirely new copies you must override the clone() method to create copies of the referenced objects.
Hope that helps.
------------------
Jane Griscti
Sun Certified Programmer for the Java� 2 Platform