求解器返回错误：如何处理它

Question

我收到提示：

Exception in thread "main" java.lang.IllegalArgumentException: bound must be positive 
    at java.util.Random.nextInt(Random.java:388) 
    at MortalCoilSolver.findSolutionPath(MortalCoilSolver.java:63) 
    at MortalCoilSolver.solve(MortalCoilSolver.java:48) 
    at MortalCoilSolver.go(MortalCoilSolver.java:33) 
    at MortalCoilSolver.main(MortalCoilSolver.java:22) 

使用代码：

import java.io.*; 
import java.net.URL; 
import java.util.Random; 

// program to solve the puzzle at http://www.hacker.org/coil/ 
public class MortalCoilSolver { 
private static int[][] offsets = {{-1, 0}, {0, 1}, {1, 0}, {0, -1}}; 
private static char[] offNames = {'L', 'D', 'R', 'U'}; 
private Random r = new Random(); 
private static String name, pw; 
private int targetFill, boardX, boardY, startX = -1, startY = -1, board[][]; 
private String boardString; 

public static void main(String[] args) throws Exception { 
    if (args.length != 2) { 
     System.out.println("usage:\nMortalCoilSolver name pw\n"); 
     return; 
    } 
    name = args[0]; pw = args[1]; 
    MortalCoilSolver mcs = new MortalCoilSolver(); 
    while (true) { 
     mcs.go(); 
     Thread.sleep(2000); 
    } 
} 

private void go() throws Exception { 
    URL u; 
    u = new URL("http://www.hacker.org/coil/index.php?name=" + name + "&password=" + pw); 
    InputStream is = u.openStream(); 
    input2level(is); 
    System.out.println(this); 
    solve(); 
} 

public String toString() { 
    String s = ""; 
    for (int j = 0; j < boardY; j++) { 
     for (int i = 0; i < boardX; i++) { 
      s += board[i][j] > 0 ? 'X' : '.'; 
     } 
     if (j < boardY - 1) s += '\n'; 
    } 
    return s; 
} 

public boolean solve() throws Exception { 
    String path = findSolutionPath(); 
    System.out.println("solved at (" + startX + ", " + startY + ") : " + path); 
    URL u; 
    u = new URL("http://www.hacker.org/coil/index.php?name=" + name + 
      "&password=" + pw + "&path=" + path + "&x=" + startX + "&y=" + startY); 
    InputStream is = u.openStream(); 
    BufferedReader in = new BufferedReader(new InputStreamReader(is)); 
    while ((in.readLine()) != null) { } 
    is.close(); 
    return false; 
} 

private String findSolutionPath() { 
    while (true) { // search until done 
     parseBoardString(); // reset board 
     startX = r.nextInt(boardX); startY = r.nextInt(boardY); // random start 
     if (!goodSquare(startX, startY)) continue; 
     int x = startX, y = startY, fill = 1; 
     String path = ""; // remember our path 
     loop: while (true) { 
      int tdir = r.nextInt(4); // choose random direction 
      for (int dloop = 0; dloop < 3; dloop++) { 
       int dir = (dloop + tdir) % 4; 
       int offx = offsets[dir][0]; 
       int offy = offsets[dir][1]; 
       if (!goodSquare(x + offx, y + offy)) continue; // blocked 
       path += offNames[dir]; 
       while (true) { // move until we hit something 
        board[x][y] = 2; 
        x += offx; y += offy; 
        if (!goodSquare(x, y)) break; 
        if (++fill == targetFill) return path; // got it 
       } 
       x -= offx; y -= offy; // we went one too far! 
       continue loop; 
      } 
      break; 
     } 
    } 
} 

private boolean goodSquare(int x, int y) { 
    if (x < 0 || y < 0 || x >= boardX || y >= boardY) return false; 
    return (board[x][y] == 0); 
} 

private void input2level(InputStream is) throws IOException { 
    BufferedReader in = new BufferedReader(new InputStreamReader(is)); 
    String line; 
    while ((line = in.readLine()) != null) { 
     if (!line.startsWith(" <param name=\"FlashVars\"")) continue; 
     line = line.split("\"")[3]; // get just the value 
     String[] ss = line.split("(=|&)"); // split up the name value pairs 
     boardX = Integer.parseInt(ss[1]); boardY = Integer.parseInt(ss[3]); 
     board = new int[boardX][boardY]; 
     boardString = ss[5]; 
     parseBoardString(); 
    } 
    in.close(); 
} 

private void parseBoardString() { 
    int cnt = 0; 
    for (int x = 0; x < boardX; x++) 
     for (int y = 0; y < boardY; y++) { 
      int a = boardString.charAt(x + y * boardX) == 'X' ? 1 : 0; 
      board[x][y] = a; 
      cnt += a; 
     } 
    targetFill = (boardX * boardY) - cnt; // how many squares we need to fill 
} 

}

Answer 1

首先，看你的错误消息，并尝试明白它。第一行告诉你是什么错误

bound must be positive 

而下，这个问题的方法和地点 -

Random.nextInt(Random.java:388) 

这是Java库，所以看不起堆栈跟踪，直到你找到你自己的方法之一

at MortalCoilSolver.findSolutionPath(MortalCoilSolver.java:63) 

看看你的代码的63行

startX = r.nextInt(boardX); startY = r.nextInt(boardY); // random start 

把它放在一起，r.nextInt被称为零或负值boardX或boardY。快速查看你的代码表明这些值的默认值仍为0.