Java 在图形对象上绘制图像不起作用，但绘制线起作用

由于某些原因，在图形对象上绘制图像似乎不起作用，请参见Triangle->paintComponent（）方法

我会错过一些重要的东西吗？也许与不将图形对象强制转换为Graphics2D有关？透明面具

    final JFrame jFrame = new JFrame();
    jFrame.add(new Triangle());
    jFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    jFrame.setSize(500,500);
    jFrame.repaint();
    jFrame.setVisible(true);

三角形类：

public class Triangle extends JPanel {

private int x = 50;
private int y = 50;

private int width = 100;
private int length = 300;

private int direction = 0;

private BufferedImage renderedImage = null;

private Image getRenderedImage() {
    if (renderedImage == null) {
        BufferedImage image = new BufferedImage(100, 300, BufferedImage.TYPE_3BYTE_BGR);
        drawGraphics(image.getGraphics());
    }

    return renderedImage;
}

private void drawGraphics(Graphics graphics) {
    graphics.setColor(Color.BLUE);
    // left
    graphics.drawLine(
            (int) Math.round(x - (width / 2.0)), y,
            (int) x, y + length);

    // right
    graphics.drawLine(
            (int) x, y + length,
            (int) Math.round(x + (width / 2.0)), y);

    // bottom
    graphics.drawLine(
            (int) Math.round(x - (width / 2.0)), y,
            (int) Math.round(x + (width / 2.0)), y);
}

protected void paintComponent(Graphics graphics) {
    // this works
    //drawGraphics(graphics);

    // this doesn't work
    graphics.drawImage(getRenderedImage(), 0, 0, null);
}
}

---

不要使用

buffereImage=

尝试执行

renderImage=

。您将返回

renderImage

，该值为空，这就是正在绘制的内容，修复了它。谢谢您！