异常线程“main”在java中

Question

我试图做一个游戏的字体，但在开发游戏的显示java.lang.NullPointerException每当我加载它，我得到这个错误：

Exception in thread "main" java.lang.NullPointerException 
at image.ImageFont.load(ImageFont.java:78) 
at image.ImageFont.<init>(ImageFont.java:47) 
at image.ImageFontTest.init(ImageFontTest.java:26) 
at image.GameCore.run(GameCore.java:65) 
at image.ImageFontTest.main(ImageFontTest.java:11) 

我也有文件它：

ImageFontTest

public class ImageFontTest extends GameCore { 

public static void main(String[] args) { 
    new ImageFontTest().run(); 
} 

private static final long TOTAL_TIME = 6500; 

private ImageFont bigFont; 
private ImageFont medFont; 
private long remainingTime; 
private CharMovement[] charMovement; 

public void init() { 
    super.init(); 

    remainingTime = TOTAL_TIME; 
    // load image fonts 
    bigFont = new ImageFont("fonts/big"); 
    medFont = new ImageFont("fonts/medium"); 

    String message = "Good Times!"; 
    int stringWidth = medFont.stringWidth(message); 
    charMovement = new CharMovement[message.length()]; 
    for (int i=0; i<message.length(); i++) { 
     charMovement[i] = new CharMovement(message, i, 
      (screen.getWidth() - stringWidth)/2, 
      screen.getHeight()/2); 
    } 
} 

public void update(long elapsedTime) { 
    remainingTime -= elapsedTime; 
    if (remainingTime <= 0) { 
     stop(); 
    } 
} 

public void draw(Graphics2D g) { 
    // erase background 
    g.setColor(Color.BLACK); 
    g.fillRect(0,0,screen.getWidth(), screen.getHeight()); 

    // draw some aligned text 
    medFont.drawString(g, "Left", 0, 0, 
     ImageFont.LEFT | ImageFont.TOP); 
    medFont.drawString(g, "Center", screen.getWidth()/2, 0, 
     ImageFont.HCENTER | ImageFont.TOP); 
    medFont.drawString(g, "Right", screen.getWidth(), 0, 
     ImageFont.RIGHT | ImageFont.TOP); 

    // draw seconds remaining 
    String timeLeft = "" + (remainingTime/1000); 
    bigFont.drawString(g, timeLeft, 0, screen.getHeight()); 

    // draw moving characters 
    double p = (double)(TOTAL_TIME - remainingTime)/TOTAL_TIME; 
    for (int i=0; i<charMovement.length; i++) { 
     charMovement[i].draw(g, p); 
    } 
} 

/** 
    Simple animation class to animate a character along a 
    path. 
*/ 
public class CharMovement { 
    char ch; 
    Point[] path; 

    public CharMovement(String s, int charIndex, int x, int y) { 
     int stringWidth = medFont.stringWidth(s); 
     for (int i=0; i<charIndex; i++) { 
      x+=medFont.charWidth(s.charAt(i)); 
     } 
     ch = s.charAt(charIndex); 

     path = new Point[4]; 

     // start offscreen 
     path[0] = new Point(x-2000, y); 

     // move to the center of the screen and pause there 
     path[1] = new Point(x, y); 
     path[2] = path[1]; 

     // "explode" at a random angle far away 
     double angle = Math.random() * 2 * Math.PI; 
     double distance = 1000 + 1000*Math.random(); 
     path[3] = new Point(
      (int)Math.round(x + Math.cos(angle) * distance), 
      (int)Math.round(y + Math.sin(angle) * distance)); 
    } 

    /** 
     Draws this character in the path, where p is the 
     location in the path from 0 to 1. 
    */ 
    public void draw(Graphics g, double p) { 
     int points = path.length - 1; 
     int index = (int)(p*points); 
     p = p * points - index; 
     Point start = path[index % path.length]; 
     Point goal = path[(index + 1) % path.length]; 
     int x = (int)Math.round(goal.x * p + start.x * (1-p)); 
     int y = (int)Math.round(goal.y * p + start.y * (1-p)); 
     medFont.drawChar(g, ch, x, y); 
    } 
} 
} 

ImageFont

/** 
The ImageFont class allows loading and drawing of text 
using images for the characters. 

Reads all the png images in a directory in the form 
"charXX.png" where "XX" is a decimal unicode value. 

Characters can have different widths and heights. 
*/ 
public class ImageFont { 

public static final int HCENTER = 1; 
public static final int VCENTER = 2; 
public static final int LEFT = 4; 
public static final int RIGHT = 8; 
public static final int TOP = 16; 
public static final int BOTTOM = 32; 

private char firstChar; 
private Image[] characters; 
private Image invalidCharacter; 


/** 
    Creates a new ImageFont with no characters. 
*/ 
public ImageFont() { 
    this(null); 
    firstChar = 0; 
    characters = new Image[0]; 
} 


/** 
    Creates a new ImageFont and loads character images from 
    the specified path. 
*/ 
public ImageFont(String path) { 
    if (path != null) { 
     load(path); 
    } 

    // make the character used for invalid characters 
    invalidCharacter = 
     new BufferedImage(10, 10, BufferedImage.TYPE_INT_RGB); 
    Graphics g = invalidCharacter.getGraphics(); 
    g.setColor(Color.RED); 
    g.fillRect(0,0,10,10); 
    g.dispose(); 
} 


/** 
    Loads the image files for each character from the 
    specified path. For example, if "../fonts/large" 
    is the path, this method searches for all the images 
    names "charXX.png" in that path, where "XX" is a 
    decimal unicode value. Not every character image needs 
    to exist; you can only do numbers or uppercase letters, 
    for example. 
*/ 
public void load(String path) throws NumberFormatException { 
    // in this directory: 
    // load every png file that starts with 'char' 
    File dir = new File(path); 
    File[] files = dir.listFiles(); 

    // find min and max chars 
    char minChar = Character.MAX_VALUE; 
    char maxChar = Character.MIN_VALUE; 
    for (int i=0; i<files.length; i++) { 
     int unicodeValue = getUnicodeValue(files[i]); 
     if (unicodeValue != -1) { 
      minChar = (char)Math.min(minChar, unicodeValue); 
      maxChar = (char)Math.max(maxChar, unicodeValue); 
     } 
    } 

    // load the images 
    if (minChar < maxChar) { 
     firstChar = minChar; 
     characters = new Image[maxChar - minChar + 1]; 
     for (int i=0; i<files.length; i++) { 
      int unicodeValue = getUnicodeValue(files[i]); 
      if (unicodeValue != -1) { 
       int index = unicodeValue - firstChar; 
       characters[index] = new ImageIcon(
        files[i].getAbsolutePath()).getImage(); 
      } 
     } 

    } 

} 


private int getUnicodeValue(File file) 
    throws NumberFormatException 
{ 
    String name = file.getName().toLowerCase(); 
    if (name.startsWith("char") && name.endsWith(".png")) { 
     String unicodeString = 
      name.substring(4, name.length() - 4); 
     return Integer.parseInt(unicodeString); 
    } 
    return -1; 
} 


/** 
    Gets the image for a specific character. If no image for 
    the character exists, a special "invalid" character image 
    is returned. 
*/ 
public Image getImage(char ch) { 
    int index = ch - firstChar; 
    if (index < 0 || index >= characters.length || 
     characters[index] == null) 
    { 
     return invalidCharacter; 
    } 
    else { 
     return characters[index]; 
    } 
} 


/** 
    Gets the string width, in pixels, for the specified string. 
*/ 
public int stringWidth(String s) { 
    int width = 0; 
    for (int i=0; i<s.length(); i++) { 
     width += charWidth(s.charAt(i)); 
    } 
    return width; 
} 


/** 
    Gets the char width, in pixels, for the specified char. 
*/ 
public int charWidth(char ch) { 
    return getImage(ch).getWidth(null); 
} 


/** 
    Gets the char height, in pixels, for the specified char. 
*/ 
public int charHeight(char ch) { 
    return getImage(ch).getHeight(null); 
} 


/** 
    Draws the specified string at the (x, y) location. 
*/ 
public void drawString(Graphics g, String s, int x, int y) { 
    drawString(g, s, x, y, LEFT | BOTTOM); 
} 


/** 
    Draws the specified string at the (x, y) location. 
*/ 
public void drawString(Graphics g, String s, int x, int y, 
    int anchor) 
{ 
    if ((anchor & HCENTER) != 0) { 
     x-=stringWidth(s)/2; 
    } 
    else if ((anchor & RIGHT) != 0) { 
     x-=stringWidth(s); 
    } 
    // clear horizontal flags for char drawing 
    anchor &= ~HCENTER; 
    anchor &= ~RIGHT; 

    // draw the characters 
    for (int i=0; i<s.length(); i++) { 
     drawChar(g, s.charAt(i), x, y, anchor); 
     x+=charWidth(s.charAt(i)); 
    } 
} 


/** 
    Draws the specified character at the (x, y) location. 
*/ 
public void drawChar(Graphics g, char ch, int x, int y) { 
    drawChar(g, ch, x, y, LEFT | BOTTOM); 
} 


/** 
    Draws the specified character at the (x, y) location. 
*/ 
public void drawChar(Graphics g, char ch, int x, int y, 
    int anchor) 
{ 
    if ((anchor & HCENTER) != 0) { 
     x-=charWidth(ch)/2; 
    } 
    else if ((anchor & RIGHT) != 0) { 
     x-=charWidth(ch); 
    } 

    if ((anchor & VCENTER) != 0) { 
     y-=charHeight(ch)/2; 
    } 
    else if ((anchor & BOTTOM) != 0) { 
     y-=charHeight(ch); 
    } 
    g.drawImage(getImage(ch), x, y, null); 
} 
} 

我看到它说这个问题是在ImageFont加载，但我不知道如何解决它。

Answer 1

Exception in thread "main" java.lang.NullPointerException 
at image.ImageFont.load(ImageFont.java:78) 

您有一个NPE（空指针异常）：这意味着您已经使用了一个尚未初始化的变量或对象。

例子：

Button b; 
b.setText("Text in my button"); // NULL POINTER EXCEPTION: b is a button but which button?!? 

解决方案

Button b = new Button(); 
b.setText("Text in my button"); // b now is a brand new button and it can be used. 

你先生有这样的问题:)