Java Glossary : opaque

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opaque

In Swing, you can do a JComponent.setOpaque( true ) to notify everyone that when your component paints, it covers the entire region with no background showing through, so there is no need for Swing to clear the background before calling your paintComponent method. This replaces the AwT update/paint mechanism.

The symptom of failing to call setOpaque( true ) is flicker, where the image gets repeatedly repainted to the background colour. The symptom of calling setOpaque( true ), when you should not are artifacts -- little bits of left over painting from other work in where your component should be. These are areas you did not paint, which should have been background.

If in your TableCellRenderer you create your own JLabels to return, rather than using the one from DefaultTableCellRenderer, make sure you call JLabel.setOpaque( true ) or else your JLabel.setBackground will be ignored.

gotchas ¤ paint ¤ update

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