while循环中读取文件时的BufferedReader输入始终为空

Question

我正在尝试读取文本文件并创建数组。使用文件的前2个值设置数组，这些值出现在第一行。然后将文件中的所有剩余项添加到数组中。由于某种原因，我的数组也总是为空。需要做哪些修正才能使其正常运行？

public static Grid createGrid(String filename) throws IOException {
        BufferedReader input;
        String inputLine;
        char[][] grid;
        Grid currentGrid;
        int currentLine = 0;
        try{
            input = new BufferedReader(new FileReader(filename));
            inputLine = input.readLine();
            String[] tokens = inputLine.split(" ");
            if(tokens.length != 2){
                throw new IllegalArgumentException();
            }
            int height = Integer.parseInt(tokens[0]);
            int width = Integer.parseInt(tokens[1]);
            grid = new char[height][width];
            while(inputLine != null){ // Giving me (Condition 'inputLine != null' is always 'true') in ide
                System.out.println(inputLine);
                inputLine = input.readLine();
                for(int i = 0; i < inputLine.length() - 1; i++){
                    char currentGem = inputLine.charAt(i);
                    grid[currentLine][i] = currentGem;
                }
                currentLine++;
            }
            input.close();
            currentGrid = new Grid(grid);
        }
        catch(IOException e){
            System.out.println(e.getMessage());
            currentGrid = null;
        }
        return currentGrid; // Giving me (Value 'currentGrid' is always 'null') in ide
    }

Answer 1

在您的代码中...

while（inputLine！=null）

...将始终为true，因为inputline是您的字符串并且在运行此检查时它将始终具有值。原因是，一旦您将null读取到inputline中（当您到达文件末尾时），而不是运行循环检查，您将在尝试运行下一行代码时抛出nullPointerException...用于（int i=0；i 。这又将导致 currentgrid始终为 null，因为在这一点上它仍然声明为 null。

public static Grid createGrid(String filename) throws IOException {
    Grid currentGrid = null;
    try {
        BufferedReader input = new BufferedReader(new FileReader(filename));
        String inputLine = input.readLine();
        String[] tokens = inputLine.split(" ");
        if(tokens.length != 2){
            throw new IllegalArgumentException();
        }
        int height = Integer.parseInt(tokens[0]);
        int width = Integer.parseInt(tokens[1]);
        char[][] grid = new char[height][width];
        int currentLine = 0;
        inputLine = input.readLine(); // added before while
        while(inputLine != null) {
            System.out.println(inputLine);
            for(int i = 0; i < inputLine.length() - 1; i++){
                char currentGem = inputLine.charAt(i);
                grid[currentLine][i] = currentGem;
            }
            currentLine++;
            inputLine = input.readLine(); // last line in while
        }
        input.close();
        currentGrid = new Grid(grid);
    }
    catch(IOException e) {
        System.out.println(e.getMessage());
        currentGrid = null;
    }
    return currentGrid; 
}