java - 空指针异常

Question

这个问题已经有答案了:

What is a NullPointerException, and how do I fix it? (12 个回答)

已关闭 7 年前。

这是我的代码我遇到的问题是数组越界错误。查看代码我似乎无法弄清楚问题出在哪里

//姓名:凯文·兰德尔 //用户名:KRandall //描述:该程序将创建地牢和相关声音

public class Dungeon
{
private  Cell[][] dungeon;
private Config config;
private int width;
private int height;
private Hero hero;
private Stats stats;
// Construct a new dungeon of the specified size.
// NOTE: The dungeon starts out completely empty and won't be usable 
// until other methods have been run the constructed object:
//  1) set() to initialize each Cell in the dungeons 2D array
//  2) addHero() to put a hero in the dungeon
//  3) addItem() to add keys and gems to the dungeon   
public Dungeon(Config config, int width, int height)
{
    this.config = config;
    this.width = width;
    this.height =height;
    dungeon = new Cell[width][height]; 
    stats = new Stats();
}

// Adds the specified hero to the dungeon
public void addHero(Hero hero)
{
    this.hero = hero;

}    

public int getHeight()
{
    return height;
}
public int getWidth ()
{
    return width;
}
public int getCount  ( Item item)
{
    int count = 0;
    for(int i = 0; i < width; i++){
        for(int j = 0; j < height; j++){
            dungeon[i][j].containsItem(item);
            if (dungeon[i][j].containsItem(item))
                count++;
        }

    }
    return count;
} 
public double getElapsedTime()
{
    return stats.elapsedTime();

}
// Setup a given grid location based on a string:
//  "W" = wall
//  "S" = secret passage
//  "D" = closed door
//  "O" = open door
//  "-" = dirt floor
public void set(int cellX, int cellY, String str)
{  
    String walls = config.wallImage();
    String pass = config.passageImage();
    String cDoor = config.closedDoorImage();
    String oDoor = config.openDoorImage();
    String floor = config.passageImage();
    String [] rock = config.rockImages();
    switch (str)
    {
    case "R": dungeon[cellX][cellY] = new CellRock(config);
    break;
    case "W": dungeon[cellX][cellY] = new Cell(walls);
    break;
    case "S": dungeon[cellX][cellY] = new CellPassage(pass);
    break;
    case "D": dungeon[cellX][cellY] = new CellDoor(oDoor,cDoor,true);
    break;
    case "O": dungeon[cellX][cellY] = new CellDoor(oDoor,cDoor,false);
    break;
    case "-": dungeon[cellX][cellY] = new CellPassage(floor);
    break;
    }
    hero.collectItem(dungeon[cellX][cellY].treasure);
    dungeon[cellX][cellY].treasure = Item.NONE;

}


// Add the specified item to a random location in the dungeon.
// The item can only be added to a cell that is passable (i.e.
// not a wall or a locked door). The location must not already
// have an item and items can't be added on top of the hero.     
public void addItem(Item item)
{   
    boolean placed = false;
    while(!placed){

        int xPos = (int)(Math.random()* width);
        int yPos = (int)(Math.random()* height);
        if (!(hero.getX() == xPos && hero.getY() == yPos)){
            if(dungeon[xPos][yPos].attemptToAdd(item)){
                placed = true;
            }

        }

    }

}

// Make the Hero execute the specified action.
// Currently this is attempting to move north, south, east, or west.
// If the hero succeeds in moving, play the walking sound.
// If the action would take the hero into an impassable cell OR 
// off the dungeon grid, play the hit wall sound.
public void execute(Action action)
{ 
    int x = hero.getX();
    int y = hero.getY();

    switch (action){
    case INVALID:
        break;
    case NORTH: y++;if (y < height && dungeon[x][y].attemptToMove(hero)){StdAudio.play(config.walkSound());hero.setLocation(x, y);}
    else StdAudio.play(config.hitWallSound());
    break;
    case SOUTH: y--;if (y >=0 &&dungeon[x][y].attemptToMove(hero)){StdAudio.play(config.walkSound());hero.setLocation(x, y);}
    else StdAudio.play(config.hitWallSound());
    break;
    case EAST:x++; if (x < width && dungeon[x][y].attemptToMove(hero)){StdAudio.play(config.walkSound());hero.setLocation(x, y);}
    else StdAudio.play(config.hitWallSound());
    break;
    case WEST:x--; if (x >= 0 && dungeon[x][y].attemptToMove(hero)){StdAudio.play(config.walkSound());hero.setLocation(x, y);}
    else StdAudio.play(config.hitWallSound());
    break;
    }

}

// Draw all the cell tiles that make up the dungeon.
// Also draws the hero.
public void draw()
{       
    for(int i = 0; i < width; i++){
        for(int j = 0; j < height; j++){
            dungeon[i][j].draw(config, i, j);
        }
    }
    hero.draw();

    StdDraw.setPenColor(StdDraw.GREEN);
    StdDraw.text(64.0,64.0 * height - 32.0,"Keys:   " + hero.numKey);
    StdDraw.setPenColor(StdDraw.BLUE);
    StdDraw.text(192.0,64 * height - 32.0,"Gems:    " + hero.numGem);
    StdDraw.setPenColor(StdDraw.RED);
    StdDraw.text(320.0, 64 * height - 32.0,"Axe:    " + hero.numAxe);
}

// Test program for Dungeon, feel free to change for your own testing needs
public static void main(String [] args)
{
    // The config object stores defaults for sizes, sounds, and images
    Config config = new Config();

    // Setup a fake 4 x 3 dungeon
    final int WIDTH = 4;
    final int HEIGHT = 3;
    Dungeon dungeon = new Dungeon(config, WIDTH, HEIGHT);
    StdDraw.setCanvasSize(WIDTH * config.cellPixels(), HEIGHT * config.cellPixels());
    StdDraw.setXscale(0, WIDTH * config.cellPixels());
    StdDraw.setYscale(0, HEIGHT * config.cellPixels());

    // Create a dungeon like:
    //  W--W
    //  W---
    //  WDW-
    dungeon.set(0, 0, "W");
    dungeon.set(1, 0, "D");
    dungeon.set(2, 0, "W");
    dungeon.set(3, 0, "-");

    dungeon.set(0, 1, "O");
    dungeon.set(1, 1, "-");
    dungeon.set(2, 1, "-");
    dungeon.set(3, 1, "-");

    dungeon.set(0, 2, "W");
    dungeon.set(1, 2, "-");
    dungeon.set(2, 2, "-");
    dungeon.set(3, 2, "W");


    Hero hero = new Hero(config, 1, 1);
    dungeon.addHero(hero);

    // Add 3 keys and 3 gems at random locations
    for (int i = 0; i < 3; i++)
    {
        dungeon.addItem(Item.KEY);
        dungeon.addItem(Item.GEM);
    }

    // Draw the sample dungeon
    dungeon.draw();
}   

}

Answer 1

dungeon = new Cell[width][height]; 

这将创建一个 Cell 对象的二维数组，并使用 null 进行初始化。所以每次访问都会给你一个异常(exception)。您需要创建 Cell 对象并自己用它们填充数组。