使用repaint（）时绘制图形而不删除它们

Question

I have a draw method and I want the drawLine to remain on the screen after I call repaint(). The fillOval will be moving, that is ok. But i want the drawLine to be redraw just on another position without deleting it.

public void paint(Graphics g) {
    super.paint(g);

    g.setColor(Color.RED);
    g.drawLine(x, y, x+10, y+10);
    g.setColor(Color.BLACK);
    g.fillOval(x - radius, y - radius, radius * 2, radius * 2);

}

Answer 1

In the repaint request, you must specify the coordinates and dimensions of the "dirty area" by using one of the following methods:

• repaint(long tm, int x, int y, int width, int height)
• repaint(Rectangle r)

Note that you'll want to override paintComponent , not paint when performing custom painting.

Answer 2

You can store the x and y of every line in a List . On each repaint() , you just redraw all the lines present in the List