Holding a reference in JAVA

[Aristotelis]

I 'm just not sure on the way java can keep a reference on an object.
If I have the following code:

MyClass A = new MyClass();
MyClass B = null;
B = A;
Does B hold a reference on A or an instance of it?And consequently, if I
change B afterwards, will this affect A?
thanks
aik_b

[Aristotelis]

"Aristotelis" <ykoto@ced.tuc.gr> wrote:
>
>I 'm just not sure on the way java can keep a reference on an object.
>If I have the following code:
>
>MyClass A = new MyClass();
>MyClass B = null;
>B = A;
>Does B hold a reference on A or an instance of it?And consequently, if I
>change B afterwards, will this affect A?
>thanks
>aik_b

Do you Have any idea of the way you could do such think??

"Aristotelis" <a@a.com> wrote:
>
>"Aristotelis" <ykoto@ced.tuc.gr> wrote:
>>
>>I 'm just not sure on the way java can keep a reference on an object.
>>If I have the following code:
>>
>>MyClass A = new MyClass();
>>MyClass B = null;
>>B = A;
>>Does B hold a reference on A or an instance of it?And consequently, if
I
>>change B afterwards, will this affect A?
>>thanks
>>aik_b
>
>Do you Have any idea of the way you could do such think??

This problem is covered in Appendix A of Bruce Eckel's free online book,
'Thinking in Java' (3rd edition), which you can download from http://www.bruceeckel.com.
That Appendix is titled 'Passing and Returning Objects'.

Essentially Java doesn't make 'deep copies' and instead holds a reference,
so in your example, if you later change A, B will also change (changing B
should not affect A however). There is a method called Object.clone() which
Eckel also talks about, and a method for 'deep copying' arrays.

[Jay]

<java.@127.0.0.1> wrote:
>
>"Aristotelis" <a@a.com> wrote:
>>
>>"Aristotelis" <ykoto@ced.tuc.gr> wrote:
>>>
>>>I 'm just not sure on the way java can keep a reference on an object.
>>>If I have the following code:
>>>
>>>MyClass A = new MyClass();
>>>MyClass B = null;
>>>B = A;
>>>Does B hold a reference on A or an instance of it?And consequently, if
>I
>>>change B afterwards, will this affect A?
>>>thanks
>>>aik_b
>>
>>Do you Have any idea of the way you could do such think??
>
>This problem is covered in Appendix A of Bruce Eckel's free online book,
>'Thinking in Java' (3rd edition), which you can download from http://www.bruceeckel.com.
>That Appendix is titled 'Passing and Returning Objects'.
>
>Essentially Java doesn't make 'deep copies' and instead holds a reference,
>so in your example, if you later change A, B will also change (changing
B
>should not affect A however). There is a method called Object.clone() which
>Eckel also talks about, and a method for 'deep copying' arrays.
>
>
Am i missing something here?
Both A and B are references to a object of type MyClass. If you must you
can think of A and B as pointers of type Myclass* in C++. Neither A nor B
is special, neither actually contains the underlying space (memory) associated
with a MyClass object. Thus 'changing B' and 'changing A' mean the same thing
- change the object (memory) referenced by B (or A) and since both A and
B refer to the same object a 'change to B' is the obviously seen as a 'change
to A'.

The JVM is responsible for keeping track of all the references to an object
- when all the references become inaccessible the underlying object becomes
'garbage' and its associated space (memory) is made available for some other
object (i.e., it is garbage collected).

[Mike]

<java.@127.0.0.1> wrote:
>
>"Aristotelis" <a@a.com> wrote:
>>
>>"Aristotelis" <ykoto@ced.tuc.gr> wrote:
>>>
>>>I 'm just not sure on the way java can keep a reference on an object.
>>>If I have the following code:
>>>
>>>MyClass A = new MyClass();
>>>MyClass B = null;
>>>B = A;
>>>Does B hold a reference on A or an instance of it?And consequently, if
>I
>>>change B afterwards, will this affect A?
>>>thanks
>>>aik_b
>>
>>Do you Have any idea of the way you could do such think??
>
>This problem is covered in Appendix A of Bruce Eckel's free online book,
>'Thinking in Java' (3rd edition), which you can download from http://www.bruceeckel.com.
>That Appendix is titled 'Passing and Returning Objects'.
>
>Essentially Java doesn't make 'deep copies' and instead holds a reference,
>so in your example, if you later change A, B will also change (changing
B
>should not affect A however). There is a method called Object.clone() which
>Eckel also talks about, and a method for 'deep copying' arrays.
>
>
Sorry, but that's wrong - changing B does affect A. They both point to the
same instance.