[英]Drawing line between two JPanels
我想在两个JPanel之间画线; 请在“ g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_ON);”中验证我的代码是否为其提供了NULL指针异常。
码::
Draw(JPanel one , JPanel two)
{
//Draw Line
Graphics2D g=null;
Graphics2D g2d = (Graphics2D) g;
g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
g2d.setColor(Color.lightGray);
2d.fillRect(0, 0, getWidth(), getHeight());
g2d.setColor(Color.black);
Stroke s = new BasicStroke(4.0f);
// For getting the points of JPanel ona and two//
int x1 = one.getX() + one.getWidth() / 2;
int y1 = one.getY() + one.getHeight() / 2;
int x2 = one.getX() + one.getWidth() / 2;
int y2 = two.getY() + two.getHeight() / 2;
//Drawing line
g2d.drawLine(x1, y1, x2, y2);
}
因为您正在将 NULL
值转换并存储到g2d
。
看下面的代码:
Graphics2D g=null;
Graphics2D g2d = (Graphics2D) g;
在第一行中, g
为NULL
。 并将其g2d
并分配给g2d
。 因此, g2d
变为NULL
,这意味着它无法使用。
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