🚀 go-pugleaf

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 Your first line:

   List copy = new ArrayList(planets);

Produces a shallow copy.  Your second line:

   Collections.copy(copy,planets);

is an expensive no-op: it merely overwrites each element
with itself.

   As for deep copies, Java itself offers very little
support for them.  In
particular, the fact that the Cloneable interface lacks a
public clone
operation makes it impossible to do a deep copy of a
collection unless you
know the element type.  For this reason, the Java
Collections Framework
offers no direct support for deep copying, but it's quite
straightforward to
do it manually if you know the element type:

    copy = new ArrayList();
    for (Iterator i=planets.iterator(); i.hasNext(); )
        copy.add(((StringBuffer)(i.next())).clone());

But this raises an interesting question: why are you using
(mutable)
StringBuffers instead of (immutable) Strings?  The names of
the planets
won't change, and if you use immutable elements, there's no
need to do a
deep copy.  In general, I believe that it's good practice to
use immutable
elements (and more generally, immutable types) wherver
possible.

         Regards,

         Josh




Werner Dubitzky wrote:

> How can I make DEEP copies of collections within the
> Collections Framework?
>
> The two approaches below make only SHALLOW copies:
>
> ...
> List copy = new ArrayList(aList);
> ...
>
> ...
> Collections.copy(destList,sourceList);
> ....
>
> Cheers.
> Mabuse

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