求助：Java代码第30行出现ArrayIndexOutOfBoundsException异常

先看报错信息：Index 4 out of bounds for length 4，发生在createQuilt方法第30行，对应代码r * block[4].length——你的block（即myBlock）只有4行，索引范围是0-3，block[4]直接越界，应该用block[0].length来获取每行的长度（假设所有行长度一致）。

除此之外，代码里还有多处会导致异常或功能错误的问题，逐一修正：

1. createQuilt方法的参数与坐标错误 #

• 第30行：block[4].length → 改为block[0].length
• else分支中placeBlock的参数顺序颠倒，应该是placeBlock(quilt, flippedBlock, ...)，原代码把flippedBlock和quilt的位置写反了
• 放置block的起始坐标计算错误，行方向应该用r * block.length，列方向用c * block[0].length，原代码的行和列逻辑搞混

修正后的createQuilt：

public static void createQuilt(char[][] quilt, char[][] block) {
    char[][] flippedBlock = createFlipped(block);

    for (int r = 0; r < 3; r++) {
        for (int c = 0; c < 4; c++) {
            if (((r + c) % 2) == 0) {
                placeBlock(quilt, block, r * block.length, c * block[0].length);
            } else {
                placeBlock(quilt, flippedBlock, r * block.length, c * block[0].length);
            }
        }
    }
}

2. placeBlock方法的循环越界 #

循环条件c <= block[r].length会导致访问block[r][block[r].length]，数组索引最大为length-1，所以改为<：

public static void placeBlock(char[][] quilt, char[][] block, int startRow, int startCol) {
    for (int r = 0; r < block.length; r++) {
        for (int c = 0; c < block[r].length; c++) { // 把<=改成<
            quilt[r + startRow][c + startCol] = block[r][c];
        }
    }
}

3. createFlipped方法的数组初始化与翻转逻辑错误 #

• 原代码blockRows = block.length - 3会导致flipped数组只有1行，完全错误，应该和原block行数一致：blockRows = block.length
• blockCols = block.length - 1错误，应该用原block的列数：blockCols = block[0].length
• 翻转逻辑错误，原代码所有行都写到flipped的同一行，应该是原第row行对应翻转后的blockRows - 1 - row行

修正后的createFlipped：

public static char[][] createFlipped(char[][] block) {
    int blockRows = block.length;
    int blockCols = block[0].length;
    char[][] flipped = new char[blockRows][blockCols];
    
    for (int row = 0; row < blockRows; row++) {
        int flippedRow = blockRows - 1 - row;
        for (int col = 0; col < blockCols; col++) {
            flipped[flippedRow][col] = block[row][col];
        }
    }

    return flipped;
}

4. displayPattern方法的行列访问颠倒 #

原代码myArray[c][r]把行和列搞反了，应该是myArray[r][c]，并且每行结束后加换行保证格式正确：

public static void displayPattern(char[][] myArray) {
    for (int r = 0; r < myArray.length; r++) {
        for (int c = 0; c < myArray[r].length; c++) {
            System.out.print(myArray[r][c]);
        }
        System.out.println();
    }
}

修正后的完整代码 #

public class BuggyQuilt {
    public static void main(String[] args) {

        char[][] myBlock = { { 'x', '.', '.', '.', '.' },
                             { 'x', '.', '.', '.', '.' },
                             { 'x', '.', '.', '.', '.' },
                             { 'x', 'x', 'x', 'x', 'x' } };
        char[][] myQuilt = new char[3 * myBlock.length][4 * myBlock[0].length];

        createQuilt(myQuilt, myBlock);

        displayPattern(myQuilt);
    }

    public static void displayPattern(char[][] myArray) {
        for (int r = 0; r < myArray.length; r++) {
            for (int c = 0; c < myArray[r].length; c++) {
                System.out.print(myArray[r][c]);
            }
            System.out.println();
        }
    }

    public static void createQuilt(char[][] quilt, char[][] block) {
        char[][] flippedBlock = createFlipped(block);

        for (int r = 0; r < 3; r++) {
            for (int c = 0; c < 4; c++) {
                if (((r + c) % 2) == 0) {
                    placeBlock(quilt, block, r * block.length, c * block[0].length);
                } else {
                    placeBlock(quilt, flippedBlock, r * block.length, c * block[0].length);
                }
            }
        }
    }

    public static void placeBlock(char[][] quilt, char[][] block, int startRow, int startCol) {
        for (int r = 0; r < block.length; r++) {
            for (int c = 0; c < block[r].length; c++) {
                quilt[r + startRow][c + startCol] = block[r][c];
            }
        }
    }

    public static char[][] createFlipped(char[][] block) {
        int blockRows = block.length;
        int blockCols = block[0].length;
        char[][] flipped = new char[blockRows][blockCols];
        
        for (int row = 0; row < blockRows; row++) {
            int flippedRow = blockRows - 1 - row;
            for (int col = 0; col < blockCols; col++) {
                flipped[flippedRow][col] = block[row][col];
            }
        }

        return flipped;
    }
}

内容的提问来源于stack exchange，提问作者Nijon Knight