硬币翻转程序

Question

I tried making a program that flips a coin(shows image of heads first and later shows image of tails) and I encountered problems trying to have the image of the coin viewed when I ran the problem; only a blank screen would show. I don't know whether this is from an improper saving method of the jpg images or from an error in the code. I also came across an error before again coding the program where I had the heads image show and tails image not show.

CoinTest.java runs coin runner and Coin.java is the class for the program.

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class CoinTest extends JPanel
implements ActionListener
{
  private Coin coin;

  public CoinTest ()
{
Image heads = (new ImageIcon("quarter-coin-head.jpg")).getImage();
Image tails = (new ImageIcon("Indiana-quarter.jpg")).getImage();
coin = new Coin(heads, tails);

Timer clock = new Timer(2000, this);
clock.start();
}

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

int x = getWidth() / 2;
int y = getHeight() / 2;
coin.draw(g, x, y);
}

 public void actionPerformed(ActionEvent e)
   {
    coin.flip();
    repaint();
   }

public static void main(String[] args)
{
JFrame w = new JFrame("Flipping coin");
w.setSize(300, 300);
w.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    CoinTest panel = new CoinTest();
    panel.setBackground(Color.WHITE);
    Container c = w.getContentPane();
    c.add(panel);

    w.setVisible(true);
  }
}

Now the actual Coin class.

import java.awt.Image;
import java.awt.Graphics;

public class Coin
{
private Image heads;
private Image tails;
private int side = 1;

public Coin(Image h, Image t)
{
    heads = h;
    tails = t;
}

//flips the coin
public void flip()
{
    if (side == 1)
        side = 0;
    else
        side = 1;
}

//draws the appropriate side of the coin - centered  in the JFrame
public void draw(Graphics g, int x, int y)
{
    if (side == 1)
    g.drawImage(heads, heads.getWidth(null)/3, heads.getHeight(null)/3, null);
    else 
    g.drawImage(heads, tails.getWidth(null)/3, tails.getHeight(null)/3, null);
}
}

Answer 1

Firstly, ensure that both images are in the correct location to load.

Secondly, you have a typo here:

if (side == 1)
  g.drawImage(heads, heads.getWidth(null)/3, heads.getHeight(null)/3, null);
else 
  g.drawImage(heads, tails.getWidth(null)/3, tails.getHeight(null)/3, null);
              ^^^^

should be tails...

Answer 2

The width and height of the applet are coded in the tag. The code that draws the applet uses the two methods to get these values at run time. So now, different tags can ask for the same applet to paint different sized rectangles. The source code does not need to be recompiled for different sizes.