Question

免责声明：这是家庭作业，所以我不是在寻找一个确切的答案，因为我想自己这样做。 我必须从填充了双精度的文本文件中读取矩阵并放入2D数组中。我目前正努力找到我的问题究竟在哪里，因为我知道如何将内置的Java Scanner用于普通数组。我下面的代码总是给我一个NullPointerException错误，这意味着我的矩阵 2D数组是空的。

public Matrix(String fileName){
    //reads first double and puts it into the [1][1] category
    //then moves on to the [1][2] and so on
    //once it gets to the end, it switches to [2][1]
    Scanner input = new Scanner(fileName);
    int rows = 0;
    int columns = 0;
    while(input.hasNextLine()){
        ++rows;
        Scanner colReader = new Scanner(input.nextLine());
        while(colReader.hasNextDouble()){
            ++columns;
        }
    }
    double[][]matrix = new double[rows][columns];
    input.close();

    input = new Scanner(fileName);
    for(int i = 0; i < rows; ++i){
        for(int j = 0; j < columns; ++j){
            if(input.hasNextDouble()){
                matrix[i][j] = input.nextDouble();
            }
        }
    }
}

我的文字档案：

1.25 0.5 0.5 1.25
0.5 1.25 0.5 1.5
1.25 1.5 0.25 1.25

Answer 1

您的代码有一些错误 - 因为它是作业，我会尽可能地坚持您的原始设计：

public Matrix(String fileName){

    //First issue - you are opening a scanner to a file, and not its name.
    Scanner input = new Scanner(new File(fileName)); 
    int rows = 0;
    int columns = 0;

    while(input.hasNextLine()){
        ++rows;
        columns = 0; //Otherwise the columns will be a product of rows*columns
        Scanner colReader = new Scanner(input.nextLine());
        while(colReader.hasNextDouble()){
            //You must "read" the doubles to move on in the scanner.
            colReader.nextDouble();
            ++columns;
        }
        //Close the resource you opened!
        colReader.close();
    }
    double[][]matrix = new double[rows][columns];
    input.close();

    //Again, scanner of a file, not the filename. If you prefer, it's
    //even better to declare the file once in the beginning.
    input = new Scanner(new File(fileName));
    for(int i = 0; i < rows; ++i){
        for(int j = 0; j < columns; ++j){
            if(input.hasNextDouble()){
                matrix[i][j] = input.nextDouble();
            }
        }
    }
}

请注意评论 - 总体而言，您距离功能代码不远，但错误很重要。

将填充有双精度的文本文件读入二维数组

1 个答案: