Re: a question about alias of reference

From:

Patricia Shanahan <pats@acm.org>

Newsgroups:

comp.lang.java.programmer

Date:

Fri, 16 Jul 2010 13:10:04 -0700

Message-ID:

<LcudnT9F6Lw8Id3RnZ2dnUVZ_oadnZ2d@earthlink.com>

Eric Sosman wrote:

On 7/16/2010 3:47 PM, www wrote:

Person tom = new Person("Tom");

Person tim = new Person("Tim");

List<Person> peopleList = new ArrayList<Person>();

peopleList.add(tom);
peopleList.add(tim);

for(Person p : peopleList)
{
if(p.getName().equalsIgnoreCase("Tom"))
{
p = null;
}
}

now, I expect the reference tom will be null, but it is not. Why? I
thought the reference p is just an alias of reference tom. Both are
pointing to the same object. Setting p to null equals to setting tom to
null.

Write your address on a piece of yellow paper; call that paper
`tim'. Write it again on a piece of white paper; call that one `p'.
Erase what's written on the white paper. Is the yellow paper now
blank?

Good analogy. It can also be used for the second question. Go chalk "30"
on the door of the house at the address on the white paper. Later, go to
the address on the yellow paper, and see what number is on the door.

Patricia