Question

I wrote my own ListCellRenderer (code below) which gets my cells transparent.
Now if I run this, every single time I click on a listitem, it becomes more whiter than before. Could it be, that the JList always add’s this new JLabel – that I created – and overlays the last one?

    jListPriority.setOpaque(true);
        jListPriority.setBackground(new Color(255, 255, 255, 10));
        jListPriority.setBorder(BorderFactory.createLineBorder(new Color(250, 250, 250)));

        jListPriority.setCellRenderer(new ListCellRenderer() {

                private JLabel label = new JLabel();

                public Component getListCellRendererComponent(JList list, Object value,   
                                 int index, boolean isSelected, boolean cellHasFocus) {

                    label.setOpaque(true);
                    label.setText(value.toString());
                    label.setForeground(new Color(250, 250, 250));
                    label.setFont(new Font("Lucida Grande", Font.PLAIN, 13));
                    label.setBorder(BorderFactory.createMatteBorder(0, 0, 1, 0, new Color(250, 250, 250, 50)));
                    label.setPreferredSize(new Dimension(label.getPreferredSize().width, label.getPreferredSize().height + 3));

                    if (isSelected) {
                        label.setBackground(new Color(255, 255, 255, 20));
                    } else {
                        label.setBackground(new Color(255, 255, 255, 10));
                    }

                    return label;
                }
            });

Answer 1

The default composite for Graphics2D uses the AlphaComposite.SRC_OVER rule, so the result is expected. You’ll need to specify a suitable mode for your desired effect. You may get some ideas from this example.