当我尝试运行此程序时，为什么会有（java.lang.ArrayIndexOutOfBoundsException：5）异常？

Question

public class number_of_islands {
    public static void main(String[] args) {
        number_of_islands tester = new number_of_islands();
        char[][] testData = {{'1', '1', '1', '1', '0'}, 
                            {'1', '1', '0', '1', '0'},
                            {'1', '1', '0', '0', '0'},
                            {'0', '0', '0', '0', '0'}};
        System.out.println(tester.numIslands(testData));
    }

    public int numIslands (char[][] grid) {
        if (grid == null || grid.length == 0) {
            throw new IllegalArgumentException("Invalid argument");
        }

        int res = 0;
        for (int i = 0; i < grid.length; i++) {
            for (int j = 0; i < grid[i].length; j++) {
                if ((grid[i][j] == '0')
                   /* the line below is where the above error occurs */
                   ||((i > 0) && (grid[i - 1][j] == '1'))
                   || ((j > 0) && (grid[i][j - 1] == '1'))) {
                    continue;
                }
                res++;
            }
        }
        return res;
    }
}

In the code above, the numIslands function accepts an 2-d array as the input and compute something, but there is an array out of bounds error in the line below the comment, I have checked to let i > 0 and j > 0, why the question still there?

Thanks!

Answer 1

Just make these small changes in for loops

for (int i = 0; i < grid.length; i++) {
        for (int j = 0; j < grid[i].length; j++) {
...

Your condition in the second for loop was "i < grid[i].length"