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anotherArrayList = (ArrayList<Something>) oneArrayList.clone();
anotherArrayList.get(0).makeSomeChange();

Will the change made in the second line make effect on
oneArrayList.get(0)?

xz wrote:
> anotherArrayList = (ArrayList<Something>) oneArrayList.clone();
> anotherArrayList.get(0).makeSomeChange();
>
> Will the change made in the second line make effect on
> oneArrayList.get(0)?

clone is a shallow clone not a deep clone so yes.

Arne

Arne Vajhøj wrote:
> xz wrote:
>> anotherArrayList = (ArrayList<Something>) oneArrayList.clone();
>> anotherArrayList.get(0).makeSomeChange();
>>
>> Will the change made in the second line make effect on
>> oneArrayList.get(0)?
>
> clone is a shallow clone not a deep clone so yes.
>
> Arne

Arne:

I know that it says in the docs that ArrayList.clone() is a shallow copy
and that the elements themselves are not copied. Why then does the
following code produce the following results (or have I gone completely
around the bend today?).

import java.util.*;

public class test9 {
public static void main(String[] args) {
ArrayList<Integer> list1 = new ArrayList<Integer>();
list1.add(10);
list1.add(11);
list1.add(12);
ArrayList list2 = (ArrayList)list1.clone();
list1.set(0,20);
list1.add(30);
for (int i=0; i<list1.size(); i++)
System.out.print(list1.get(i)+" ");
System.out.println();
for (int i=0; i<list2.size(); i++)
System.out.print(list2.get(i)+" ");
}
}

C:\Documents and Settings\Knute Johnson>java test9
20 11 12 30
10 11 12

--

Knute Johnson
email s/nospam/knute/

On Aug 3, 8:28 pm, Knute Johnson <nos...@rabbitbrush.frazmtn.com>
wrote:
> Arne Vajhøj wrote:
> > xz wrote:
> >> anotherArrayList = (ArrayList<Something>) oneArrayList.clone();
> >> anotherArrayList.get(0).makeSomeChange();
>
> >> Will the change made in the second line make effect on
> >> oneArrayList.get(0)?
>
> > clone is a shallow clone not a deep clone so yes.
>
> > Arne
>
> Arne:
>
> I know that it says in the docs that ArrayList.clone() is a shallow copy
> and that the elements themselves are not copied. Why then does the
> following code produce the following results (or have I gone completely
> around the bend today?).
>
> import java.util.*;
>
> public class test9 {
> public static void main(String[] args) {
> ArrayList<Integer> list1 = new ArrayList<Integer>();
> list1.add(10);
> list1.add(11);
> list1.add(12);
> ArrayList list2 = (ArrayList)list1.clone();
> list1.set(0,20);
> list1.add(30);

These modify the cloned list, not the Integer objects. Try replacing
the Integers with StringBuffers, and change the set line to actually
edit the string buffer, i.e. list1.get(0).append("foobar");

Then your first list output should show the first item with "foobar"
on the end and your fourth added item; your second list output should
still omit the fourth item but also have the first item have "foobar"
on the end.

Knute Johnson wrote:
> Arne Vajhøj wrote:
>> xz wrote:
>>> anotherArrayList = (ArrayList<Something>) oneArrayList.clone();
>>> anotherArrayList.get(0).makeSomeChange();
>>>
>>> Will the change made in the second line make effect on
>>> oneArrayList.get(0)?
>>
>> clone is a shallow clone not a deep clone so yes.
>>
>> Arne
>
> Arne:
>
> I know that it says in the docs that ArrayList.clone() is a shallow copy
> and that the elements themselves are not copied. Why then does the
> following code produce the following results (or have I gone completely
> around the bend today?).
>
> import java.util.*;
>
> public class test9 {
> public static void main(String[] args) {
> ArrayList<Integer> list1 = new ArrayList<Integer>();
> list1.add(10);
> list1.add(11);
> list1.add(12);
> ArrayList list2 = (ArrayList)list1.clone();
> list1.set(0,20);
> list1.add(30);
> for (int i=0; i<list1.size(); i++)
> System.out.print(list1.get(i)+" ");
> System.out.println();
> for (int i=0; i<list2.size(); i++)
> System.out.print(list2.get(i)+" ");
> }
> }
>
> C:\Documents and Settings\Knute Johnson>java test9
> 20 11 12 30
> 10 11 12
>

The difference between a deep and shallow clone is difficult to see if
you only add immutable objects, such as Integer:

import java.util.*;

public class ListCloneTest {
public static void main(String[] args) {
ArrayList<StringBuilder> list1 = new ArrayList<StringBuilder>();
list1.add(new StringBuilder("aaa "));
ArrayList list2 = (ArrayList) list1.clone();
StringBuilder builder = list1.get(0);
builder
.append("Both lists point to the same StringBuilder");
for (int i = 0; i < list1.size(); i++)
System.out.print(list1.get(i) + " ");
System.out.println();
for (int i = 0; i < list2.size(); i++)
System.out.print(list2.get(i) + " ");
}
}

aaa Both lists point to the same StringBuilder
aaa Both lists point to the same StringBuilder

Patricia

On Aug 3, 7:28 pm, Knute Johnson <nos...@rabbitbrush.frazmtn.com>
wrote:
> Arne Vajhøj wrote:
> > xz wrote:
> >> anotherArrayList = (ArrayList<Something>) oneArrayList.clone();
> >> anotherArrayList.get(0).makeSomeChange();
>
> >> Will the change made in the second line make effect on
> >> oneArrayList.get(0)?
>
> > clone is a shallow clone not a deep clone so yes.
>
> > Arne
>
> Arne:
>
> I know that it says in the docs that ArrayList.clone() is a shallow copy
> and that the elements themselves are not copied. Why then does the
> following code produce the following results (or have I gone completely
> around the bend today?).
>
> import java.util.*;
>
> public class test9 {
> public static void main(String[] args) {
> ArrayList<Integer> list1 = new ArrayList<Integer>();
> list1.add(10);
> list1.add(11);
> list1.add(12);
> ArrayList list2 = (ArrayList)list1.clone();
this line copies every item in list1 into list2 such that
list1.get(i) = list2.get(i) for i = 0, 1, 2,
which means, two references (0th item in list1 and 0th item in list2)
point to the same thing, but they themselves are not identical.

> list1.set(0,20);
now you changed the 0th item in list1, in other words, you let the the
0th item in list1, which is a reference, point to another thing (20).
This process has nothing to do with list2, meaning 0th item in list2
still points to 10.

> list1.add(30);
> for (int i=0; i<list1.size(); i++)
> System.out.print(list1.get(i)+" ");
> System.out.println();
> for (int i=0; i<list2.size(); i++)
> System.out.print(list2.get(i)+" ");
> }
>
> }
>
> C:\Documents and Settings\Knute Johnson>java test9
> 20 11 12 30
> 10 11 12
>

However, as I konw ArrayList can only deal with classes, e.g. Integer,
but not primitive types like int. How come your code compiles?

xz wrote:
>> ArrayList<Integer> list1 = new ArrayList<Integer>();
>> list1.add(10);
>> list1.add(11);
>> list1.add(12);

> However, as I konw ArrayList can only deal with classes, e.g. Integer,
> but not primitive types like int. How come your code compiles?

Newer Java versions (1.5+) can auto convert between int and Integer.

Arne

Knute Johnson wrote:
> Arne Vajhøj wrote:
>> clone is a shallow clone not a deep clone so yes.

> I know that it says in the docs that ArrayList.clone() is a shallow copy
> and that the elements themselves are not copied. Why then does the
> following code produce the following results (or have I gone completely
> around the bend today?).

As other has already stated, then you are changing the references
in the lists not the objects pointed to by the references.

The docs are correct.

Arne

Do you mean now wherever you can use Integer, you can use int, and
vice versa?

That's cool. Didn't know that before.

On Aug 3, 10:11 pm, Arne Vajhøj <a...@vajhoej.dk> wrote:
> xz wrote:
> >> ArrayList<Integer> list1 = new ArrayList<Integer>();
> >> list1.add(10);
> >> list1.add(11);
> >> list1.add(12);
> > However, as I konw ArrayList can only deal with classes, e.g. Integer,
> > but not primitive types like int. How come your code compiles?
>
> Newer Java versions (1.5+) can auto convert between int and Integer.
>
> Arne

Arne Vajhøj wrote:
> Knute Johnson wrote:
>> Arne Vajhøj wrote:
>>> clone is a shallow clone not a deep clone so yes.
>
>> I know that it says in the docs that ArrayList.clone() is a shallow
>> copy and that the elements themselves are not copied. Why then does
>> the following code produce the following results (or have I gone
>> completely around the bend today?).
>
> As other has already stated, then you are changing the references
> in the lists not the objects pointed to by the references.
>
> The docs are correct.
>
> Arne

Thanks very much everybody. I was confused when I wrote the test code
because it did copy the references. That was not as I expected. Using
a mutable object it is immediately obvious though.

--

Knute Johnson
email s/nospam/knute/