为什么运行paint()? 为什么背景透明?怎样做到不透明?

Question

import java.awt.Graphics;import java.awt.Color;import javax.swing.JFrame;import java.util.Random;public class Colors extends JFrame{private static final Random rand=new Random();public Colors(){super("Colors");setSize(640,480);setVisible(true);setBackground(Color.white);}public void paint( Graphics draw ){draw.setColor(Color.black);draw.fillRect(0, 0, 640, 480);draw.drawString("Colors ", 50, 50);Color newColor = new Color(40,60,80);draw.setColor(newColor);draw.drawArc(100,100,50,50,0,-180);newColor = new Color(rand.nextInt(256),rand.nextInt(256),rand.nextInt(256));draw.setColor(newColor);draw.drawRect(250,100,50,50);newColor = new Color(rand.nextInt(256),rand.nextInt(256),rand.nextInt(256));draw.setColor(newColor);draw.fillRect(450,200,50,50);}public static void main( String args[] ){Colors test = new Colors();}}

Answer 1

public class Colors extends JFrame {

private static final Random rand = new Random();

public Colors() {
super("Colors");
final JPanel panel = new JPanel() {

public void paint(Graphics draw) {

// draw.setColor(Color.black);
// draw.fillRect(0, 0, 640, 480);
draw.drawString("Colors ", 50, 50);

Color newColor = new Color(40, 60, 80);
draw.setColor(newColor);
draw.drawArc(100, 100, 50, 50, 0, -180);

newColor = new Color(rand.nextInt(256), rand.nextInt(256), rand.nextInt(256));
draw.setColor(newColor);
draw.drawRect(250, 100, 50, 50);

newColor = new Color(rand.nextInt(256), rand.nextInt(256), rand.nextInt(256));
draw.setColor(newColor);
draw.fillRect(450, 200, 50, 50);
}
};
Action action = new AbstractAction() {

public void actionPerformed(ActionEvent e) {
panel.repaint();
}
};
Timer timer = new Timer(250, action);
timer.setRepeats(true);
timer.start();
this.setContentPane(panel);
setSize(640, 480);
setVisible(true);
setBackground(Color.white);

}

public static void main(String args[]) {
Colors test = new Colors();
}
}

透明了，你自己填充了一次黑色就黑了。pait在窗体变化的时候就回自动重画。如果你自己调用repaint时候也回重画。

Answer 2

当组建第一次加载的时候会自动调用paint（）
paint是系统回调函数，当你以后在想调用paint的时候，直接写repaint（）就可以了，repaint会调用paint。
背景透明?不会啊，JFrame默认是透明的，你加上setVisible(true);
就不会了啊，我这看是黑色的，你自己在看看吧