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Problem: I don't know where to put my painting code.Problem: The stuff I paint doesn't show up.
- Painting code belongs in the
paintComponent
method of any component descended fromJComponent
. See Overview of Custom Painting for details.Problem: The background of my applet shows up, but the foreground stuff doesn't show up.
- Check whether your component is showing up at all. Solving Common Component Problems should help you with this.
Problem: My component's foreground shows up, but its background is invisible. The result is that one or more components directly behind my component are unexpectedly visible.
- Did you make the mistake of performing painting directly in a
JApplet
subclass? If so, then your contents will be covered by the content pane that is automatically created for everyJApplet
instance. Instead, create another class that performs the painting and then add that class to theJApplet
's content pane. See Painting for more information on how painting in Swing works.
- Make sure your component is opaque.
JPanel
s, for example, are opaque by default. To make other components such asJLabel
s opaque, you must invokesetOpaque(true)
on them.- If your custom component extends
JPanel
or a more specializedJComponent
descendant, then you can paint the background by invokingsuper.paintComponent
before painting the contents of your component.- You can paint the background yourself using this code at the top of a custom component's
paintComponent
method:g.setColor(getBackground()); g.fillRect(0, 0, getWidth(), getHeight()); g.setColor(getForeground());Problem: I used
setBackground
to set my component's background color, but it seemed to have no effect.
- Most likely, your component isn't painting its background, either because it's not opaque or your custom painting code doesn't paint the background. If you set the background color for a
JLabel
, for example, you must also invokesetOpaque(true)
on the label to make the label's background be painted. For more help, see the preceding problem.Problem: I'm using the exact same code as a tutorial example, but it doesn't work. Why?
Problem: How do I paint thick lines? patterns?
- Is the code executed in the exact same method as the tutorial example? For example, if the tutorial example has the code in the example's
paintComponent
method, then this method might be the only place where the code is guaranteed to work.If you don't see your problem in this list, see Solving Common Component Problems and Solving Common Layout Problems.
- The JavaTM 2D API provides extensive support for implementing line widths and styles, as well as patterns for use in filling and stroking shapes. See the 2D Graphics trail for more information on using the Java 2D API.
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