Swing下的paint、repaint、validate、update、updateUI

Paint() - this method holds instructions to paint this component. Actually, in Swing, you should change paintComponent() instead of paint(), as paint calls paintBorder(), paintComponent() and paintChildren(). You shouldn't call this
method directly, you should call repaint() instead.

repaint() - this method can't be overridden. It controls the update() -> paint() cycle. You should call this method to get a component to repaint itself. If you have done anything to change the look of the component, but not it's size ( like changing color,
animating, etc. ) then call this method.

validate() - This tells the component to lay itself out again and repaint itself. If you have done anything to change the size of the component or any of it's children(adding, removing, resizing children), you should call this method... I think that calling
revalidate() is preferred to calling validate() in Swing, though...

update() - This method is in charge of clearing the component and calling paint(). Again, you should call repaint() instead of calling this method directly... If you need to do fast updates in animation you should override this method to just call the paint()
method.

updateUI() - Call this method if you have changed the pluggable look & feel for a component after it has been made visible.

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