Java Swing revalidate vs repaint

Question

I m putting together a Swing application where I often want to replace the contents of a JPanel  To do this  I m calling removeAll    then adding my new content  then calling revalidate     However I m finding that the old content is still actually visible  though obscured by the the new content   If I add a call to repaint   in addition to revalidate    it works as expected   I m sure on other occasions I ve experienced that just calling revalidate   is enough   So basically my question is - should I need to call both functions and if not  when should I call each of them

User · Accepted Answer

You need to call repaint   and revalidate    The former tells Swing that an area of the window is dirty  which is necessary to erase the image of the old children removed by removeAll     the latter tells the layout manager to recalculate the layout  which is necessary when adding components   This should cause children of the panel to repaint  but may not cause the panel itself to do so  see this for the list of repaint triggers    On a more general note  rather than reusing the original panel  I d recommend building a new panel and swapping them at the parent

User · Answer

Any time you do a remove   or a removeAll    you should call    validate      repaint      after you have completed add   ing the new components   Calling validate   or revalidate   is mandatory when you do a remove   - see the relevant javadocs   My own testing indicates that repaint   is also necessary  I m not sure exactly why

User · Answer

revalidate is called on a container once new components are added or old ones removed   this call is an instruction to tell the layout manager to reset based on the new component list   revalidate will trigger a call to repaint what the component thinks are  dirty regions    Obviously not all of the regions on your JPanel are considered dirty by the RepaintManager   repaint is used to tell a component to repaint itself   It is often the case that you need to call this in order to cleanup conditions such as yours

User · Answer

yes you need to call      repaint        revalidate    when you call removeAll   then you have to call repaint   and revalidate

User · Answer

revalidate   just request to layout the container  when you experienced simply call revalidate   works  it could be caused by the updating of child components bounds triggers the repaint   when their bounds are changed during the re-layout  In the case you mentioned  only component removed and no component bounds are changed  this case no repaint   is  accidentally  triggered

[java] Java Swing revalidate() vs repaint()

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