java - 插入二维字符串数组时出现空指针异常

Question

我有一个名为 input1.txt 的文件，其内容如下:

a b c d

bd

c d

d e

我想读取它并将它们放入二维字符串数组中。我已经为它编写了代码。但它显示空指针异常。错误可能出在哪里？下面是我的代码:

我在 graphNodes[i][j] = s; 行中收到异常

BufferedReader br = null;
    BufferedReader cr = null;
    int lines = 0;
    try {
        br = new BufferedReader(new FileReader(filename));
        try {
            while (br.readLine() != null) {
                lines++;
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    } catch (FileNotFoundException e1) {
        e1.printStackTrace();
    }
    List<String> nodes = new ArrayList<String>();
    String[][] graphNodes = new String[lines][];
    String[] line = new String[lines];
    int i = 0;
    int j = 0, x = 0;
    try {
        cr = new BufferedReader(new FileReader(filename));
        while (cr.readLine() != null) {
            line[x] = cr.readLine();
            System.out.println("Line is: " + line[x]);
            String[] letters = line[x].split(" ");
            for (String s : letters) {
                 System.out.println("Letter is " + s);
                graphNodes[i][j] = s;
                j++;
            }
            i++;
            x++;
        }
    } catch (IOException e) {
        e.printStackTrace();
    }

Answer 1

graphNodes 缺少列长度

String[][] graphNodes = new String[lines][];

在你的问题中，一旦你得到字母，你就可以初始化二维数组的列

String[] letters = line[x].split(" ");
graphNodes[i] = new String[letters.length];