Re: Best way to force a JComponent to repaint itself

Knute Johnson <>
Wed, 13 Aug 2008 22:31:52 -0700
zerg wrote:

Peter Duniho wrote:

On Wed, 13 Aug 2008 21:35:50 -0700, zerg <> wrote:

I begin to suspect that there's some sort of unwritten code here that
forbids the giving of a straight answer.

Forgive us if we suspect that there's some sort of unwritten code
among questioners that forbids the inspection of the relevant
documentation before asking a question.

Suspect what you will, but I did indeed examine the JComponent API docs,
and there were three public methods associated with repainting -- not
counting that repaint() had two overloads.

I may have been somewhat biased by what I was specifically searching
for, namely a no-argument method for "repaint the whole component". It
looks like maybe that is simply lacking.

Either you never bothered to even read the documentation, or there's
something more to your question than simply "what's the API-approved
to force a repaint?" Either way, your question isn't a well-formed one.

Anything that I say is well-formed, and I am not in the mood to be
publicly insulted by you or anyone else here. I came here asking for
advice in good faith and I don't appreciate being treated in such a manner.

If I understand your follow-up correctly, you simply have some sort of
custom component that needs to be redrawn when internal state changes
that would be reflected visually. Assuming that's the correct
interpretation, then the documentation does in fact provide all of the
necessary information you need.

Perhaps it does, but it is less than clear, for whatever reason.
Probably because the API docs are organized around a
what-this-thingamajig-does scheme, while the tutorial, though organized
around a how-to-do-X scheme, rather glosses over repainting of
components, other than to make it clear that to paint custom stuff
(rather than just at custom times) you override paintComponent.

If there's something about the documentation that is confusing you,
there's no shame in being specific about that and asking for help with

That's more or less what I did, except that I simply asked directly for
the answer to the question that I had, instead of for clarification of a
particular bit of the docs.

If you have read the documentation and need some help, then say so and
be specific about what kind of help you need.

Fine. From now on, when I have a highly specific question like "what is
the best way to force a JComponent to repaint itself?", instead of just
asking "what is the best way to force a JComponent to repaint itself?",
I will do as you advise here and say "I've read the documentation, but
still have a question: what is the best way to force a JComponent to
repaint itself?" -- satisfied?

If you simply ask a question that the documentation does in fact
 answer, the most obvious explanation is that you haven't bothered
to look at the documentation at all.

Sometimes the most obvious explanation is wrong. Regardless, what the
explanation is is not relevant. The question I asked was about
JComponent painting, not about what the most likely explanation was for
why I asked the question. If you'd please just focus on the actual
content of a post asking a question, and refrain from speculating about
why the poster might have asked it or other unimportant things like that
that have no bearing on things, I think people might appreciate that.
People post questions here to get them answered, not to get sidetracked
into unrelated topics to satisfy your curiosity as to peoples' motives
in asking questions or for any similar such reason.

It's best to just take peoples' questions at face value, and give them a
simple, correct answer that they can apply immediately. I don't know
about you, but when I have a question, I'm generally interested in
getting an answer as quickly as possible, and one that can be applied
immediately. Therefore I've already read all the obviously-relevant
documentation, since if it has the answer in a clear and unambiguous
form that will get me moving much quicker than waiting for someone to
reply on a Usenet group. If that doesn't suffice, then I ask a question
here, and at that point I'm not going to be pleased if instead of the
one iteration of post-reply that it SHOULD take for me to get an answer
back, it ends up taking two or three because people want to satisfy
their idle curiosity as to why I'm asking the question, and of course if
they simply answered it straight away, I might go away and not answer
their questions! So they withhold my answer until they have satisfied
their curiosity -- wasting my time and everyone's bandwidth with matters
that are tangential, at best, to the purpose of this newsgroup.

Please don't do that any more. I find it annoying. If I ask "how to do
X", please just tell me, in simple terms, how to do X. If you think the
documentation should have answered it for me, well, apparently it
didn't. If you want, you can certainly point to the bit of the
documentation that you think unambiguously answers the question and ask
me why I didn't apparently one of find it relevant enough to look at or
find it clear and certain enough to use, AT THE SAME TIME as supplying
the actual answer. Then, since I'll have the answer I need to continue
with my work without delay, I am likely to be able to find some time
later to satisfy your curiosity a bit, and therefore I am likely to
answer, and to be much less annoyed and irritated when I do.

Thank you.

You can get as mad as you want but people are really trying to help you.
  And having been around here for a while, when someone asks "What
method do I use to repaint() a JComponent," we get sort of suspicious
because repainting is rarely the solution to anything.

And whether you believe it or not there IS a no-arg repaint() method.
It belongs to JComponent.

So, this is my last attempt to help you. Answer the questions or not,
your choice.

1) Are you updating your ListModel on the EDT?

2) Are you doing long running tasks on the EDT (in a listener for example)?

3) Are you adding or removing components to your JList?


Knute Johnson
email s/nospam/knute2008/

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