所以，立即想到两件事......

So, two things come to mind immediately...

首先，不要使用 getBounds ， Grapghics 上下文已经转换为组件 x / y 位置，所以你加倍了。相反，只需使用 0x0 并提供宽度和高度 ，类似......

First, don't use getBounds, the Grapghics context is already translated to the components x/y position, so you're doubling that up. Instead, simply use 0x0 and provide the width and height, something like...

graphics2d.fillRect(0, 0, getWidth(), getHeight());

另外，请记住，大多数Swing组件默认是不透明的，包括 JList ， JScrollPane 并且它是 JViewport ，如果你需要将它们设置为透明希望他们能够完全看透。

Also, remember, most Swing components are opaque by default, this includes the JList, JScrollPane and it's JViewport, you need to set these to be transparent if you want them to be see through at all.

此外， JList 的默认渲染器也使用渲染器如果你想让物品透明，你需要能够提供自己的物品......

Also, the "default" renderer that the JList uses also renderers it self as opaque, so you need to be able to supply your own if you want the items to be transparent...

import java.awt.AlphaComposite;
import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagLayout;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.imageio.ImageIO;
import javax.swing.DefaultListCellRenderer;
import javax.swing.DefaultListModel;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.border.EmptyBorder;

public class Test {

    public static void main(String[] args) {
        new Test();
    }

    public Test() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                DefaultListModel<String> model = new DefaultListModel<>();
                model.addElement("Bananas");
                model.addElement("Apples");
                model.addElement("Pears");
                model.addElement("Grapes");
                model.addElement("Tim Tams");

                JList list = new JList(model);
                list.setCellRenderer(new DefaultListCellRenderer() {

                    @Override
                    public Component getListCellRendererComponent(JList<?> list, Object value, int index, boolean isSelected, boolean cellHasFocus) {
                        super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus);
                        setOpaque(isSelected);
                        return this;
                    }

                });
                list.setOpaque(false);
                JScrollPane sp = new JScrollPane(list);
                sp.setOpaque(false);
                sp.getViewport().setOpaque(false);

                TranslucentPane tp = new TranslucentPane();
                tp.setLayout(new GridBagLayout());
                tp.setLayout(new BorderLayout());
                tp.add(sp);

                JFrame frame = new JFrame("Testing");
                frame.setContentPane(new BackgroundPane());
                frame.setLayout(new GridBagLayout());
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(tp);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TranslucentPane extends JPanel {

        private float alpha = 0.75f;

        public TranslucentPane() {
            setOpaque(false);
            setBorder(new EmptyBorder(5, 5, 5, 5));
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            g2d.setComposite(AlphaComposite.SrcOver.derive(alpha));

            g2d.setColor(getBackground());
            g2d.fillRect(0, 0, getWidth(), getHeight());
            g2d.dispose();
        }

    }

    public class BackgroundPane extends JPanel {

        private BufferedImage background;

        public BackgroundPane() {
            try {
                background = ImageIO.read(new File("C:\\Users\\shane\\Dropbox\\MegaTokyo\\thumnails\\megatokyo_omnibus_1_3_cover_by_fredrin-d4oupef.jpg"));
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(background.getWidth(), background.getHeight());
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            int x = (getWidth() - background.getWidth()) / 2;
            int y = (getHeight() - background.getHeight()) / 2;
            g.drawImage(background, x, y, this);
        }

    }

}