在循环对象时遇到空指针数组。我该如何捕捉？

Question

当我循环穿过数组时，我正在遇到一个无效的指针。是否可以进行测试，以找出可能导致此错误的原因……也许为什么在需要时没有价值？该系统停在Maptiles [0] [33]。这是代码：

import java.lang.*;
import java.util.*;
import java.io.*;

public class Map {

MapTile[][] mapTiles;
String imageMap;
String rawMap;

// constructor 
public Map() {
    imageMap = "Map_DragonShrine.jpg";
    rawMap = "Dragon_Shrine.map";
    mapTiles = new MapTile[22][34];
}


// methods
public void loadMapFile() {

    rawMap = file2String(rawMap);

    // array used to hold columns in a row after spliting by space
    String[] mapCols = null;
    // split map using 'bitmap' as delimiter
    String[] mapLines = rawMap.split("bitmap");  
    // assign whatever is after 'bitmap'
    rawMap = mapLines[1];
    // split string to remove comment on the bottom of the file
    mapLines = rawMap.split("#");
    // assign final map
    rawMap = mapLines[0].trim();
    mapLines = rawMap.split("\\n+");

    for(int x = 0; x < mapLines.length; x++) {
        rawMap = mapLines[x] ;
        mapCols = rawMap.split("\\s+");            
        for(int y = 0; y < mapCols.length; y++) {
            mapTiles[x][y] = new MapTile(mapCols[y]);   
        }            
    }   
}       

public void getTileFeatures() {
}

public void checkFeature() {
    for(int x = 0; x < mapTiles.length; x++) {
        for(int y = 0; y < mapTiles[x].length; y++) {
            makeTile(x, y, mapTiles[x][y].getFeature());
            //  java.lang.NullPointerException at mapTiles[0][33]
        }
    }
}

public String file2String(String filename) 
{          
    try{ 
        FileReader fileReader = new FileReader(filename); 
        String fileContents = ""; 
        int i ; 

        while((i =  fileReader.read())!=-1){ 
            char ch = (char)i; 

            fileContents = fileContents + ch;  
        }//end while 

        // System.out.println(fileContents); 
        return fileContents; 
    }
    catch(Exception e){
        System.out.println("File failed to load:" + e); 
        return "Error " + e; 
    } 

}//end file2String

private void makeTile(int x, int y, String features)
{
    System.out.println("line1 " + y + " test");
    //         mapTiles[x][y] = new MapTile();//Assumes your Map class has an array of MapTile objects called mapTiles
    if(features.contains("w")){   mapTiles[x][y].SOLID = true; }
    System.out.println("line2 " + y + " test");
    if(features.contains("s")){   mapTiles[x][y].STATUE = true; }
    System.out.println("line3 " + y + " test");
    if(features.contains("A")){   mapTiles[x][y].VICTORY_A = true; }
    System.out.println("line4 " + y + " test");
    if(features.contains("B")){   mapTiles[x][y].VICTORY_B = true; }
    System.out.println("line5 " + y + " test");
    if(features.contains("a")){   mapTiles[x][y].START_A = true; }
    System.out.println("line6 " + y + " test");
    if(features.contains("b")){   mapTiles[x][y].START_B = true; }
    System.out.println("line7 " + y + " test");
    if(features.contains("h")){   mapTiles[x][y].HAUNTED = true; }
    System.out.println("line8 " + y + " test");
    if(features.contains("d")){   mapTiles[x][y].DIFFICULT = true; }
    System.out.println("line9 " + y + " test");
    if(features.contains("c")){   mapTiles[x][y].SACRED_CIRCLE = true; }
    System.out.println("line10 " + y + " test");
    if(features.contains("u")){   mapTiles[x][y].SUMMONING_CIRCLE = true; }
    System.out.println("line11 " + y + " test");
    if(features.contains("x")){   mapTiles[x][y].EXIT_A = true; }
    System.out.println("line12 " + y + " test");
    if(features.contains("z")){   mapTiles[x][y].EXIT_B = true; }
    System.out.println("line13 " + y + " test");
}//End makeTile

}

Answer 1

您应该使用您的Maptile 2D阵列初始化 mapLines 目的。现在，您假设它将始终为22x34。

这很容易引起原因，其中一些地图图块未初始化。它也可能引起索引。

您的错误将归结为此。在某个地方，您不会在Maptile数组中初始化该索引。

Answer 2

使用Junit，Mockito等单元测试工具来测试您的课程。这样您可以设置 MapTile[][] 具有不同的值并对其进行运行测试。可以找到有关Mockito的信息 这里