Moving object instead references

Question

I want to copy an object into a matrix, and then equal that object to zero. But it something goes wrong, I suspect this is because only a reference is copied into the matrix, and not the object itself. And when I remove the object, the reference is obsolete. Is there a way to avoid this? I tried implenting the Cloneable interface in the object, and then putting a clone in the matrix, but it still doesn't work. Thanks

Answer 1

Your conception seems like C program. Be careful to do Object programmation.
In Java, remember that you have only references (equivalent to pointers in C).
In java you manipulate only the references through the variables.
An object is never set to null, only the variables which contains references to this object. The object is still here but not reachable.
Look this code :
MyObject var1 = new MyObject();
MyObject var2 = var1;
var1 = null;
Now let see how the program works :
new MyObject() create an instance of the class MyObject and store it at the adress 2000 (for example).
MyObject var1 = new MyObject();
In the created variable var1, the adress of the newly created object will be stored. var1 <-- 2000
MyObject var2 = var1;
We create a new variable var2 in which we store the value of the variable var1 i.e. : 2000 : var2 <-- 2000
var1 = null;
In the variable var1 the value is set to null : var1 <-- null.
At this moment the variable var1 contains no reference (null) and var2 still contains 2000 the adress of the object in memory.
I hope it is clearer for you,
Denis