Re: Setter ignored on collection

 Daniel Pitts <>
Tue, 14 Aug 2007 13:01:14 -0700
On Aug 14, 6:17 am, Patricia Shanahan <> wrote:

LT wrote:

I remember reading somthing about the behaviour exhibetet by the
program below (where a private collection is altered without going
through its accessor). But cannot seam to find the info anymore - can
someone enlightenme as to why this works:

Class for test
public class TestMe {
   private Set<String> values = new HashSet<String>();
   private int called = 0;
   public Set<String> getValues() {
           return values;


Making values private but providing this implementation of getValues
means the caller cannot change which Set values references, but can
change the membership.

If you want the caller to be able to view, but not change, the set:

public Set<String> getValues() {
   return Collections.unmodifiableSet(values);


This gives the caller a view of the set that will reflect changes you
make to it, but does not give the caller any power to add or remove


Alternatively, if you want the caller to have their own version of the
set to play with

public Set<String> getValues() {
   return new HashSet<String>(values);

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