Question

java中的drawLine方法怎么重新画线的时候保留刚才画的线？帮我看看下面的程序该怎么改才能实现？

static class getPanel extends JPanel {

private int x = 200;

private int y = 200;

private int x2 = x ;

private int y2 = y ;

public getPanel() {

addKeyListener(new KeyAdapter() {

@Override

public void keyPressed(KeyEvent arg0) {

int xtemp;

int ytemp;

switch (arg0.getKeyCode()) {

case KeyEvent.VK_UP:

xtemp=x2;

ytemp=y2;

x=xtemp;

y=ytemp;

x2=x;

y2-=50;

break;

case KeyEvent.VK_DOWN:

xtemp = x2;

ytemp = y2;

x = xtemp;

y = ytemp;

x2 = x;

y2 += 50;

break;

case KeyEvent.VK_LEFT:

xtemp = x2;

ytemp = y2;

x = xtemp;

y = ytemp;

x2 -= 50;

y2 = y;

break;

case KeyEvent.VK_RIGHT:

xtemp = x2;

ytemp = y2;

x = xtemp;

y = ytemp;

x2 += 50;

y2 = y;

break;

default:

break;

}

repaint();

}

});

}

protected void paintComponent(Graphics g) {

super.paintComponent(g);

g.setColor(Color.BLACK);

g.drawLine(x, y, x2, y2);

}

}

}

Answer 1

你把 super.paintComponent(g); 去除看看。

追问

果然可以了，能简单解释一下为什么吗？谢谢了

追答

super.paintComponent()方法会重画组件，你画在上面的图形都没有保存，当然就没有了。所以复杂一点的画板程序，都会创建一个以上的集合以保存图形信息（保存为点或线段的形式），以便在重画组件时把原先画上去的图形也画出来。当然程序也要复杂繁琐许多。

追问

明白了，谢谢了

追答

不用客气，大家互相帮忙，共同进步！