Question

我为自己做了一个相当基本的游戏。 Java Swing的新手，但不是Cpp。解决手头的问题。

当我开始运行GUI应用程序时，我用Null Pointer Exception拍摄并给出了它们发生的四个链接（我使用Eclipse作为我的IDE）。但是当我看着它们时，我发现它们周围没有任何问题。

所以我来看看你们中是否有人能发现我无法找到的东西。

此类从源文件夹中抓取图片并设置用于移动的键。

import java.awt.event.KeyEvent;
import java.awt.Image;
import javax.swing.ImageIcon;

public class SPRITES 
{
private int x_sped;
private int y_sped;
private int x;
private int y;
private Image sprite;

public SPRITES()
{
    ImageIcon pine = new ImageIcon(this.getClass().getResource("Untitled.png")); //exception here, line 17
    sprite = pine.getImage();
    x = 0;
    y = 0;
}

public void move()
{
    x += x_sped;
    y += y_sped;
}

public int getX()
{
    return x;
}

public int getY()
{
    return y;
}

public Image getImage()
{
     return sprite;
}

public void keyPressed(KeyEvent e)
{
    int key = e.getKeyCode();

    if(key == KeyEvent.VK_A)
    {
        x_sped = -1;
    }

    if(key == KeyEvent.VK_D)
    {
        x_sped = 1;
    }

    if(key == KeyEvent.VK_W)
    {
        y_sped = -1;
    }

    if(key == KeyEvent.VK_S)
    {
        y_sped = 1;
    }
}

public void keyReleased(KeyEvent e)
{
int key = e.getKeyCode();

    if(key == KeyEvent.VK_A)
    {
        x_sped = 0;
    }

    if(key == KeyEvent.VK_D)
    {
        x_sped = 0;
    }

    if(key == KeyEvent.VK_W)
    {
        y_sped = 0;
    }

    if(key == KeyEvent.VK_S)
    {
        y_sped = 0;
    }
}
}

第二个用于完成框架设置，完全制作框架并完成机芯的制作。

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import javax.swing.JPanel;
import javax.swing.Timer;

public class Stage extends JPanel implements ActionListener
{
private static final long serialVersionUID = 1L;
private Timer start_stop;
private SPRITES player;
public Stage()
{
    addKeyListener(new TAdapter());
    setFocusable(true);
    setBackground(Color.black);
    setDoubleBuffered(true);

    player = new SPRITES();

    start_stop = new Timer(5, this);
    start_stop.start();

}

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

    Graphics2D G2D = (Graphics2D) character;
    G2D.drawImage(player.getImage(), player.getX(), player.getY(), this);

    Toolkit.getDefaultToolkit().sync();
    character.dispose();
}

public void actionPerformed(ActionEvent arg0) 
{
    player.move();
    repaint();
}

private class TAdapter extends KeyAdapter
{
    public void keyReleased(KeyEvent e)
    {
        player.keyReleased(e);
    }

    public void keyPressed(KeyEvent e)
    {
        player.keyPressed(e);
    }
}
}

这最后一个应该把它们绑在一起......我知道如何修复异常。

import javax.swing.JFrame;

@SuppressWarnings("serial")
public class Framing extends JFrame
{
public Framing()
{
    add(new Stage()); 

    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setSize(600, 600);
    setLocationRelativeTo(null);
    setTitle("FLY");
    setResizable(false);
    setVisible(true);
}
public static void main(String[] args)
{
        new Framing();
}
}

导致这些异常的原因是什么？我该如何解决问题以及我应该做些什么来避免再次发生这种情况？

Answer 1

我认为你误读了eclipse中的堆栈跟踪。除了第一个（顶部的那个）之外的所有链接都是调用堆栈，它显示了对你得到nullpointer异常的地方的调用。

Which fit because the code:
new Framing()
Calls
add(new Stage())
which calls
player = new SPRITES();
Which calls
ImageIcon pine = new ImageIcon(this.getClass().getResource("Untitled.png"));

这是你的nullpointer异常的地方。我的猜测是getResources（“Untitled.png”）;返回null，然后导致ImageIcon构造函数抛出nullpointer异常。

使用三个类的GUI应用程序的空指针异常

1 个答案: