令人困惑的 Java 语法

Question

我正在尝试将以下代码（来自 Wikipedia）从 Java 转换为 JavaScript ：

/*
 * 3 June 2003, [[:en:User:Cyp]]:
 *     Maze, generated by my algorithm
 * 24 October 2006, [[:en:User:quin]]:
 *     Source edited for clarity
 * 25 January 2009, [[:en:User:DebateG]]:
 *     Source edited again for clarity and reusability
 * 1 June 2009, [[:en:User:Nandhp]]:
 *     Source edited to produce SVG file when run from the command-line
 *
 * This program was originally written by [[:en:User:Cyp]], who
 * attached it to the image description page for an image generated by
 * it on en.wikipedia. The image was licensed under CC-BY-SA-3.0/GFDL.
 */

import java.awt.*;
import java.applet.*;
import java.util.Random;

/* Define the bit masks */
class Constants {
    public static final int WALL_ABOVE = 1;
    public static final int WALL_BELOW = 2;
    public static final int WALL_LEFT = 4;
    public static final int WALL_RIGHT = 8;
    public static final int QUEUED = 16;
    public static final int IN_MAZE = 32;
}

public class Maze extends java.applet.Applet {
    /* The width and height (in cells) of the maze */
    private int width;
    private int height;
    private int maze[][];
    private static final Random rnd = new Random();

    /* The width in pixels of each cell */
    private int cell_width;

    /* Construct a Maze with the default width, height, and cell_width */
    public Maze() {
 this(20,20,10);
    }

    /* Construct a Maze with specified width, height, and cell_width */
    public Maze(int width, int height, int cell_width) {
 this.width = width;
 this.height = height;
 this.cell_width = cell_width;
    }

    /* Initialization method that will be called when the program is
     * run from the command-line. Maze will be written as SVG file. */
    public static void main(String[] args) {
 Maze m = new Maze();
 m.createMaze();
 m.printSVG();
    }

    /* Initialization method that will be called when the program is
     * run as an applet. Maze will be displayed on-screen. */
    public void init() {
 createMaze();
    }

    /* The maze generation algorithm. */
    private void createMaze(){
 int x, y, n, d;
 int dx[] = { 0, 0, -1, 1 };
 int dy[] = { -1, 1, 0, 0 };

 int todo[] = new int[height * width], todonum = 0;

 /* We want to create a maze on a grid. */
 maze = new int[width][height];

 /* We start with a grid full of walls. */
 for (x = 0; x < width; ++x) {
     for (y = 0; y < height; ++y) {
  if (x == 0 || x == width - 1 || y == 0 || y == height - 1) {
      maze[x][y] = Constants.IN_MAZE;
  } else {
      maze[x][y] = 63;
  }
     }
 }

 /* Select any square of the grid, to start with. */
 x = 1 + rnd.nextInt (width - 2);
 y = 1 + rnd.nextInt (height - 2);

 /* Mark this square as connected to the maze. */
 maze[x][y] &= ~48;

 /* Remember the surrounding squares, as we will */
 for (d = 0; d < 4; ++d) {
     if ((maze[][d][][d] & Constants.QUEUED) != 0) {
  /* want to connect them to the maze. */              
  todo[todonum++] = ((x + dx[d]) << Constants.QUEUED) | (y + dy[d]);
  maze[][d][][d] &= ~Constants.QUEUED;
     }
 }

 /* We won't be finished until all is connected. */
 while (todonum > 0) {
     /* We select one of the squares next to the maze. */
     n = rnd.nextInt (todonum);
     x = todo[n] >> 16; /* the top 2 bytes of the data */
     y = todo[n] & 65535; /* the bottom 2 bytes of the data */

     /* We will connect it, so remove it from the queue. */
     todo[n] = todo[--todonum];

     /* Select a direction, which leads to the maze. */
     do {
  d = rnd.nextInt (4);
     }
     while ((maze[][d][][d] & Constants.IN_MAZE) != 0);

     /* Connect this square to the maze. */
     maze[x][y] &= ~((1 << d) | Constants.IN_MAZE);
     maze[][d][][d] &= ~(1 << (d ^ 1));

     /* Remember the surrounding squares, which aren't */
     for (d = 0; d < 4; ++d) {
  if ((maze[][d][][d] & Constants.QUEUED) != 0) {      
      /* connected to the maze, and aren't yet queued to be. */
      todo[todonum++] = ((x + dx[d]) << Constants.QUEUED) | (y + dy[d]);
      maze[][d][][d] &= ~Constants.QUEUED;
  }
     }
            /* Repeat until finished. */
        }

        /* Add an entrance and exit. */
        maze[1][1] &= ~Constants.WALL_ABOVE; 
        maze[width - 2][height - 2] &= ~Constants.WALL_BELOW;
    }

    /* Called by the applet infrastructure to display the maze on-screen. */
    public void paint(Graphics g) {
 drawMaze(g);
    }

    /* Called to write the maze to an SVG file. */
    public void printSVG() {
 System.out.format("<svg width=\"%d\" height=\"%d\" version=\"1.1\""
     + " xmlns=\"http://www.w3.org/2000/svg\">\n",
     width*cell_width, height*cell_width);
 System.out.println("  <g stroke=\"black\" stroke-width=\"1\""
      + " stroke-linecap=\"round\">");
 drawMaze(null);
 System.out.println("  </g>\n</svg>");
    }

    /* Main maze-drawing loop. */
    public void drawMaze(Graphics g) {
        int x, y;

        for (x = 1; x < width - 1; ++x) {
            for (y = 1; y < height - 1; ++y) {
                if ((maze[x][y] & Constants.WALL_ABOVE) != 0)
      drawLine(      x * cell_width,       y * cell_width,
        (x + 1) * cell_width,       y * cell_width, g);
                if ((maze[x][y] & Constants.WALL_BELOW) != 0)
      drawLine(      x * cell_width, (y + 1) * cell_width,
        (x + 1) * cell_width, (y + 1) * cell_width, g);
                if ((maze[x][y] & Constants.WALL_LEFT) != 0)
      drawLine(      x * cell_width,       y * cell_width,
              x * cell_width, (y + 1) * cell_width, g);
                if ((maze[x][y] & Constants.WALL_RIGHT) != 0)
      drawLine((x + 1) * cell_width,       y * cell_width,
        (x + 1) * cell_width, (y + 1) * cell_width, g);
     }
 }
    }

    /* Draw a line, either in the SVG file or on the screen. */
    public void drawLine(int x1, int y1, int x2, int y2, Graphics g) {
 if ( g != null ) g.drawLine(x1, y1, x2, y2);
 else System.out.format("    <line x1=\"%d\" y1=\"%d\""
          + " x2=\"%d\" y2=\"%d\" />\n", x1, y1, x2, y2);
    }
}

无论如何，当我遇到一些我不明白的问题时，我进展得相当快：

 /* Remember the surrounding squares, as we will */
 for (var d = 0; d < 4; ++d) {
     if ((maze[][d][][d] & Constants.QUEUED) != 0) {
  /* want to connect them to the maze. */              
  todo[todonum++] = ((x + dx[d]) << Constants.QUEUED) | (y + dy[d]);
  maze[][d][][d] &= ~Constants.QUEUED;
     }
 }

我不明白的是为什么“迷宫”参数后面有四组括号而不是只有两组，因为“ maze”是一个二维数组，而不是一个四维数组。

我确信这是有充分理由的。问题是，我就是不明白。

谢谢！

Answer 1

为了简单地纠正语法，这个答案和任何答案一样好。然而，为了修复算法，Leon 对此有更多见解。

---

在我看来，代码是错误的，有两组太多的方括号。 maze 被声明并初始化为二维 int 数组。没有理由它应该有更多。也许是错误信息或有错误的代码生成器的结果？

只需从数组访问中删除前面的空方括号 [] （或 ][）即可设置。

Answer 2

我有根据的猜测是缺少一些代码。删除额外的 [] 会使代码编译，但它不会生成迷宫，而是陷入无限循环

我认为 [][d][][d] 应该是迷宫[x+dx[d]][y +dy[d]]。

很明显，d 应该索引到 dx 和 dy 数组中，它们是当前单元格的邻居的偏移量，因为它总是迭代 4 次。另外todo[todonum++] = ((x + dx[d]) << Constants.QUEUED) | (y + dy[d]); 使用 dx[d] 和 dy[y] 作为到邻居的偏移量来索引迷宫数组。

我不确定这是否是最好的方法，因为当 x=0 且 dx 偏移量为 -1 时，您将遇到 OutOfBoundsException。您可能必须明确处理这些情况。

Answer 3

好的，这是 JavaScript 版本：

/*
 * 3 June 2003, [[:en:User:Cyp]]:
 *     Maze, generated by my algorithm
 * 24 October 2006, [[:en:User:quin]]:
 *     Source edited for clarity
 * 25 January 2009, [[:en:User:DebateG]]:
 *     Source edited again for clarity and reusability
 * 1 June 2009, [[:en:User:Nandhp]]:
 *     Source edited to produce SVG file when run from the command-line
 * 7 January, 2011 [[:en:User:SharkD]]:
 *     Source converted to JavaScript
 *
 * This program was originally written by [[:en:User:Cyp]], who
 * attached it to the image description page for an image generated by
 * it on en.wikipedia. The image was licensed under CC-BY-SA-3.0/GFDL.
 */

/* Recreate a math function that exists in Java but not JavaScript. */
Math.nextInt = function (number) {
 return Math.floor(Math.random() * number)
}

/* Recreate a system function that exists in Java but not JavaScript.
 * Uncomment either WScript.Echo() or alert() depending on whether you are
 * running the script from the Windows command-line or a Web page.
 */
function println(string)
{
 // if inside Windows Scripting Host
// WScript.Echo(string)
 // if inside a Web page
 alert(string)
}

/* Define the bit masks */
var Constants =
{
 WALL_ABOVE : 1,
 WALL_BELOW : 2,
 WALL_LEFT : 4,
 WALL_RIGHT : 8,
 QUEUED : 16,
 IN_MAZE : 32
}

/* Construct a Maze with specified width, height, and cell_width */
function Maze(width, height, cell_width) {
 if (width)
  this.width = width;
 else
  this.width = 20;
 if (height)
  this.height = height;
 else
  this.height = 20;
 if (cell_width)
  this.cell_width = cell_width;
 else
  this.cell_width = 10;
 this.maze = []

 /* The maze generation algorithm. */
 this.createMaze = function()  {
  var width = this.width
  var height = this.height
  var maze = this.maze
  var x, y, n, d;
  var dx = [ 0, 0, -1, 1 ];
  var dy = [ -1, 1, 0, 0 ];

  var todo = new Array(height * width);
  var todonum = 0;

  /* We want to create a maze on a grid. */
  /* We start with a grid full of walls. */
  for (x = 0; x < width; ++x) {
   maze[x] = []
   for (y = 0; y < height; ++y) {
    if (x == 0 || x == width - 1 || y == 0 || y == height - 1) {
     maze[x][y] = Constants.IN_MAZE;
    }
    else {
     maze[x][y] = 63;
    }
   }
  }

  /* Select any square of the grid, to start with. */
  x = 1 + Math.nextInt(width - 2);
  y = 1 + Math.nextInt(height - 2);

  /* Mark this square as connected to the maze. */
  maze[x][y] &= ~48;

  /* Remember the surrounding squares, as we will */
  for (d = 0; d < 4; ++d) {
   if ((maze[x + dx[d]][y + dy[d]] & Constants.QUEUED) != 0) {
    /* want to connect them to the maze. */              
    todo[todonum++] = ((x + dx[d]) << Constants.QUEUED) | (y + dy[d]);
    maze[x + dx[d]][y + dy[d]] &= ~Constants.QUEUED;
   }
  }

  /* We won't be finished until all is connected. */
  while (todonum > 0) {
   /* We select one of the squares next to the maze. */
   n = Math.nextInt(todonum);
   x = todo[n] >> 16; /* the top 2 bytes of the data */
   y = todo[n] & 65535; /* the bottom 2 bytes of the data */

   /* We will connect it, so remove it from the queue. */
   todo[n] = todo[--todonum];

   /* Select a direction, which leads to the maze. */
   do {
    d = Math.nextInt(4);
   }
   while ((maze[x + dx[d]][y + dy[d]] & Constants.IN_MAZE) != 0);

   /* Connect this square to the maze. */
   maze[x][y] &= ~((1 << d) | Constants.IN_MAZE);
   maze[x + dx[d]][y + dy[d]] &= ~(1 << (d ^ 1));

   /* Remember the surrounding squares, which aren't */
   for (d = 0; d < 4; ++d) {
    if ((maze[x + dx[d]][y + dy[d]] & Constants.QUEUED) != 0) {      
     /* connected to the maze, and aren't yet queued to be. */
     todo[todonum++] = ((x + dx[d]) << Constants.QUEUED) | (y + dy[d]);
     maze[x + dx[d]][y + dy[d]] &= ~Constants.QUEUED;
    }
   }
   /* Repeat until finished. */
  }

  /* Add an entrance and exit. */
  maze[1][1] &= ~Constants.WALL_ABOVE; 
  maze[width - 2][height - 2] &= ~Constants.WALL_BELOW;
 }
 /* Called to write the maze to an SVG file. */
 this.printSVG = function () {
  var outstring = "<svg width=\"" + (width * cell_width) + "\" height=\"" + (height*cell_width) + "\" version=\"1.1\" xmlns=\"http://www.w3.org/2000/svg\">\n"
    + "  <g stroke=\"black\" stroke-width=\"1\" stroke-linecap=\"round\">\n"
    + this.drawMaze()
    + "  </g>\n</svg>\n";
  println(outstring)
 }
 /* Main maze-drawing loop. */
 this.drawMaze = function () {
  var x, y;
  var width = this.width;
  var height = this.height;
  var cell_width = this.cell_width
  var outstring = ""
  for (x = 1; x < width - 1; ++x) {
   for (y = 1; y < height - 1; ++y) {
    if ((this.maze[x][y] & Constants.WALL_ABOVE) != 0)
     outstring += this.drawLine(      x * cell_width,       y * cell_width,  (x + 1) * cell_width,       y * cell_width);
    if ((this.maze[x][y] & Constants.WALL_BELOW) != 0)
     outstring += this.drawLine(      x * cell_width, (y + 1) * cell_width,  (x + 1) * cell_width, (y + 1) * cell_width);
    if ((this.maze[x][y] & Constants.WALL_LEFT) != 0)
     outstring += this.drawLine(      x * cell_width,       y * cell_width,  x * cell_width, (y + 1) * cell_width);
    if ((this.maze[x][y] & Constants.WALL_RIGHT) != 0)
     outstring += this.drawLine((x + 1) * cell_width,       y * cell_width,  (x + 1) * cell_width, (y + 1) * cell_width);
   }
  }
  return outstring
 }
 /* Draw a line, either in the SVG file or on the screen. */
 this.drawLine = function (x1, y1, x2, y2) {
  return "    <line x1=\"" + x1 + "\" y1=\"" + y1 + "\" x2=\"" + x2 + "\" y2=\"" + y2 + "\" />\n";
 }
}



/* Initialization method that will be called when the program is
* run from the command-line. Maze will be written as SVG file. */
function main(args) {
 var m = new Maze();
 m.createMaze();
 m.printSVG();
}

/* execute the program */
main()

下一步是将其变成六轴 3D 迷宫并转换为 Lua，这是我的实际目标平台。 :)

PS - 我正在尝试对答案进行投票，但它告诉我我需要登录或注册，wtf？