我正在尝试实施深度优先算法来解决像这样的迷宫,其中S是第一个位置,E是“终点线”
_SW______\n
_WWW_W_WW\n
_____W__E\n
但是当它不应该发生时我得到NullPointerException。 这里是我“导入”2d数组迷宫的地方,从.txt文件中读取的迷宫进入深度第一类
public class MazeReader extends JFrame {
private static char[][] Maze;
private static ArrayList<String> mazeBuffer;
private static int startrow,startcol,finishcol,finishrow;
private final List<Integer> path = new ArrayList<Integer>();
private int pathIndex;
public MazeReader() {
setTitle("Maze");
setSize(640,480);
setLocationRelativeTo(null);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
DepthFirst.searchPath(Maze, 0, 1, path);
pathIndex = path.size() - 2;
}
public static void readTextFile(String filename) throws MazeFileWrongChar, MazeFileNumCols {
startrow=startcol=finishcol=finishrow=-1;
mazeBuffer=new ArrayList<String>();
int numCols=0;
try {
Scanner file=new Scanner(new File(filename));
while(file.hasNext()) {
String nextLine=file.nextLine().replace("\\n", "");
mazeBuffer.add(nextLine);
if(nextLine.length()>numCols) {
numCols=nextLine.length();
}
}
}catch(Exception e) {
System.out.println(filename + "there is a problem");
}
int numrows=mazeBuffer.size();
System.out.println("number of rows: "+ numrows + "\nnumber of columns: " + numCols);
Maze=new char[numrows][numCols];
for(int i=0;i<numrows;i++) {
String row = mazeBuffer.get(i);
for (int j = 0; j < numCols; j++) {
try {
if (row.length() >= j) {
Maze[i][j] = row.charAt(j);
}
} catch (Exception e) {
throw new MazeFileNumCols(j);
}
if(Maze[i][j]!=('S') && Maze[i][j]!=('W') && Maze[i][j]!=('_') && Maze[i][j]!=('E') && Maze[i][j]!=(' ') ) {
throw new MazeFileWrongChar(i,j);
}
}
}
}
这是深度优先代码
public class DepthFirst {
public static boolean searchPath(char[][] maze,int x,int y, List<Integer> path) {
if(maze[y][x]=='E') {
path.add(x);
path.add(y);
return true;
}
if(maze[y][x]=='_') {
int dx=-1;
int dy=0;
if(searchPath(maze,x+dx,y+dy,path)) {
path.add(x);
path.add(y);
return true;
}
dx = 1;
dy = 0;
if (searchPath(maze, x + dx, y + dy, path)) {
path.add(x);
path.add(y);
return true;
}
dx = 0;
dy = -1;
if (searchPath(maze, x + dx, y + dy, path)) {
path.add(x);
path.add(y);
return true;
}
dx = 0;
dy = 1;
if (searchPath(maze, x + dx, y + dy, path)) {
path.add(x);
path.add(y);
return true;
}
}
return false;
}
}
这是主要的课程
public class Main {
static MazeReader reader = new MazeReader();
public static void main(String[] args) throws MazeFileWrongChar,MazeFileNumCols {
try {
MazeReader.readTextFile("maze.txt");
reader.printMaze();
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
MazeReader view = new MazeReader();
view.setVisible(true);
}
});
} catch (MazeFileWrongChar e ) {
System.out.println(e.getMessage());
} catch(MazeFileNumCols e) {
System.out.println(e.getMessage());
}
}
}
我收到此错误
Exception in thread "main" java.lang.ExceptionInInitializerError
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:264)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:123)
Caused by: java.lang.NullPointerException
at DepthFirst.searchPath(DepthFirst.java:10)
at MazeReader.<init>(MazeReader.java:23)
我认为问题可能与在深度头等舱中启动迷宫数组时的问题有关,但我不确定。
答案 0 :(得分:0)
问题如下:由于您在Main类中将reader声明为静态变量,因此在执行主代码之前会执行其构造函数。在构造函数中,您正在访问“Maze”变量。但由于之前没有调用readTextFile,因此它为空。
它从null更改为实际数组的唯一时间是在这一行:
Maze=new char[numrows][numCols];
之前(特别是在你的构造函数中),它是null。
另外:尽量避免在整个地方使用静电。