Question

import java.awt.*;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
public class Images extends JFrame {
    public static void main(String[] args) {
    DisplayMode dm = new DisplayMode(800,600,32, DisplayMode.REFRESH_RATE_UNKNOWN);
    Images I = new Images();
    I.run(dm);
}

private Screen s;
private Image bg;
private Image pic;
private boolean nLoaded;
Animation a;

    public void run(DisplayMode dm)
    {

        nLoaded = false;
         s = new Screen();
        try{

                s.Setfullscreen(dm, this);
                LoadPics();
                MovieLoop();
                try{
                Thread.sleep(50000);    
                }catch(Exception ex){}
        }finally{
            s.restoreScreen();
        }

    }

    public void MovieLoop(){
        long startingtime = System.currentTimeMillis();
        long cumTime = startingtime;

        while(cumTime-startingtime < 5000)
        {
            long timepassed = System.currentTimeMillis() - cumTime;
            cumTime += timepassed;

            a.update(timepassed);

            Graphics g = s.getFullScreenWindow().getGraphics();
            draw(g);
            g.dispose();

            try{
            Thread.sleep(20);
            }catch(Exception ex){}

        }
    }

    public void draw(Graphics g)
    {
        g.drawImage(bg, 0,0, null);
        g.drawImage(a.getImage(),0,0,null); }


    //Create Load Pictures
    public void LoadPics()
    {
        bg = new ImageIcon("C:\\Gamepics\\BackgroundImage.jpg").getImage();
        pic = new ImageIcon("C:\\Gamepics\\SmileyIcon3.png").getImage();
        nLoaded = true;
        repaint();


    }


    public void paint(Graphics g){
        if(g instanceof Graphics2D){
            Graphics2D g2 = (Graphics2D)g;
            g2.setRenderingHint(RenderingHints.KEY_TEXT_ANTIALIASING, RenderingHints.VALUE_TEXT_ANTIALIAS_ON);
        }

        if(nLoaded)
        {
            g.drawImage(bg, 0, 0, null);
            g.drawImage(pic, 300,300, null);
        }
    }  
}

我不明白我做错了什么我已经尽力忽略了一切。我只是练习一个简单的动画，我不断得到3个空指针异常。我已经研究过最好的东西，显然java中的NullPointerExceptions与尝试获取空数组的大小有关吗？编译器没有将我的任何列表标记为问题，所以我有点困惑。任何帮助将不胜感激。所有错误都被注释掉了。它们有三个，它们在Images类

中

错误：

Exception in thread "main" java.lang.NullPointerException
at Images.MovieLoop(Images.java:45)
at Images.run(Images.java:26)
at Images.main(Images.java:8)

动画类

import java.awt.Image;
import java.util.*;
public class Animation {

private ArrayList scenes;
private int sceneindex;
private long movietime;
private long totaltime;
//CONSTRUCTOR
public Animation(){
    scenes = new ArrayList();
    totaltime =0;
    start();

}
//Add scene to array list and sets time for each scene
//For example. If you have 3 scenes you would add t to total time three times. So if you had 
//3 Scenes, one for 1s, one for 2s, one for 3s. Total time would be 6s. and you would call addscene 3 times
public synchronized void addScene(Image i, long t)
{ 
    totaltime+=t;
    scenes.add(new OneScene(i, totaltime));

}
//start animation from beggininign inignngingingnig 
public synchronized void start(){
movietime = 0;
sceneindex = 0;
}
//change scenes 


//movie time is the sum of all the time passed from last update
//If you have more than one scene. timepassed gets added to movietime.
//if movietime is greater than or equal to total time(ie. animation is complete) restart the animation
public synchronized void update(long timepassed)
{
    if(scenes.size() > 1){
        movietime += timepassed;
        if(movietime >= totaltime)
        {
            movietime = 0;
            sceneindex = 0;

        }
        while(movietime > getScene(sceneindex).endTime)
        {
            sceneindex++;
        }
    }
}

public synchronized Image getImage(){
    if(scenes.size() == 0){
        return null;}
    else{
        return getScene(sceneindex).pic;
    }
}
//Getscene
private OneScene getScene(int x){
    return (OneScene)scenes.get(x);
}
//Scenes are gonna be 
private class OneScene{
    Image pic;
    long endTime;

    public OneScene(Image pic, long endTime)
    {
        this.pic = pic;
                this.endTime = endTime;

    }
}
}

我包含了动画类，因为编译器突出显示这三个方法调用作为问题的来源

    a.update(timepassed); 
    MovieLoop(); 
     I.run(dm);

Answer 1

请注意：这是一个非常长的评论

让我们从Graphics g = s.getFullScreenWindow().getGraphics();开始 - getGraphics绝对不是一个好主意，这可以返回null。

你不应该尝试从EDT以外的任何线程更新任何UI组件，你不应该以这种方式直接绘制它，相反，你应该使用paintComponent。

您不应该dispose您自己没有创建的Graphics个上下文，这样可以防止绘制其他组件。

你应该避免覆盖paint，特别是顶层容器，如果没有其他原因，它不是双缓冲（顶级容器），你也将绘制任何其他子组件。< / p>

查看Performing Custom Painting了解详情。

您应该尝试使用ImageIO代替ImageIcon。 ImageIO如果无法读取文件，则会抛出异常，ImageIcon只是无声地失败，没有用处。

动画示例中的Java Lang nullpointer异常？

1 个答案: