从文本文件中将数组做成双精度

Question

I need to read a file of grades and input them into an array. I cant seem to figure it out though. Any suggestions. Thanks for your help :) The grades.txt file looks like this:

90.0
71.5
87.9
95.0
98.1

Code:

File file1 = new File("grades.txt");
Scanner gradesFile = new Scanner(file1);
String line = gradesFile.nextLine();

//create array
double[] array = new double[12];

//variable to increment
int u = 0;

//loop to put data into array
while(gradesFile.hasNextDouble())

    array[u] = gradesFile.nextDouble();
    u += 1;

gradesFile.close();

Answer 1

A. As @hnefatl said you need to group statements in the loop,

while(<condition>) {
   statement1;
   ...
   statementN;
}

otherwise only next one executes.

while(<condition>) statement1;
...

B. When you did String line = gradesFile.nextLine(); you got full first line from file and Scanner position is at next line if there is any.

So by doing gradesFile.hasNextDouble() after that, Scaner looks for double in next line.

If you'd like to use nextLine() and your doubles are "one-per-line" you need to work with them in a loop as:

    Scanner gradesFile = new Scanner(file1);
    // create array
    double[] array = new double[12];
    // variable to increment
    int u = 0;
    // loop to put data into array
    while (gradesFile.hasNextLine()) {
        String line = gradesFile.nextLine();
        array[u] = Double.parseDouble(line);
        u += 1;
    }

    gradesFile.close();

or if you'd like to use nextDouble() you do not mix it with nextLine()

    Scanner gradesFile = new Scanner(file1);
    // create array
    double[] array = new double[12];
    // variable to increment
    int u = 0;
    // loop to put data into array
    while (gradesFile.hasNextDouble()) {            
        array[u] = gradesFile.nextDouble();
        u++;
    }

    gradesFile.close();

Answer 2

You can simply scan the double value in your file and store in the array as below

Scanner scan;
//Data file
File file = new File(grades.txt");
//Array to store the double read from file
double[] array = new double[10];
int i =0;

try {
    scan = new Scanner(file);

    //Scan while the file has next double value
    while(scan.hasNextDouble())
    {
        //Save the double value read from text file and store to array
        array[i] = scan.nextDouble();
        i++;
    }

}catch (FileNotFoundException e) {
    e.printStackTrace();
}

To print what you have stored in your array

for(int y = 0; y < array.length;y++)
{
   System.out.println(array[y]);
}