Java: assigning values to an Array

Question

I have a method that reads in a file. The first line of the file has an integer that shows how many additional lines there are. Each additional line after that has a pair of two double values (no commas)

For Example:

4

13 15

20.2 33.5

24 38

30 31

etc.

I have two static double arrays, x and y. For each line after the first, I want to assign the first double in the set to x, and the second double in the set to y. However, i'm not 100% sure what to do how to assign. This is my code so far: (note that line is a call to another method not shown)

Scanner input = new Scanner(System.in);
    System.out.println("Enter the name of the data file.");
    fileName = input.nextLine();

    while(input.hasNext())
    {
        int num = input.nextInt(); // the first line integer
        line.x[0] = input.nextDouble(); //the additional line x coordinate
        line.y[0] = input.nextDouble(); //the additional line y coordinate
    }

The only problem is, how do I increment the value of x and y from [0] to [1], [2], 3, etc for each additional line in the file, based on what the first line int value 'num' is, so that I don't keep overwriting [0]?

For example, in the example above, the value of 'num' is 4, because there are four additional lines after it. How do I increase (+=) the value of x and y by one based on the value of num? I know this sounds stupid but I'm stumped at this point.

Something doesn't look right in your code. You show filename = input.nextLine(), then the while loop processes the input scanner. Did you instead plan to use a file reader? Or are you really reading from the console input? I'm just letting you know something looks amiss. — Alvin Bunk
– Alvin Bunk, Commented Oct 22, 2014 at 4:33

Mitesh Pathak · Accepted Answer · 2014-10-22 04:25:16Z

3

The only problem is, how do I increment the value of x and y from [0] to [1], [2], 3, etc for each additional line in the file, based on what the first line int value 'num' is, so that I don't keep overwriting [0]?

Use a counter i

int num = input.nextInt(); // the first line integer
int i = 0;

while(input.hasNext())
{
    line.x[i] = input.nextDouble(); //the additional line x coordinate
    line.y[i++] = input.nextDouble(); //the additional line y coordinate
}

answered Oct 22, 2014 at 4:25

Mitesh Pathak

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4 Comments

Jon Kiparsky Over a year ago

Just as a style note: for reasons of clarity I usually prefer to avoid using the postincrement in any complex expression. While there's no danger of this one going wrong, it's still a good rule. Hence the only difference between our two versions. :)

c0der Over a year ago

Could I also use a for loop?

Mitesh Pathak Over a year ago

Yep I would prefer a for loop, since u know the #input in advance n.

c0der Over a year ago

@MiteshPathak So this will add additional values for each line then, (like x[1], x[2], x[3],x[4] etc

Jon Kiparsky · Accepted Answer · 2014-10-22 04:26:42Z

1

  line.x[0] = input.nextDouble();

This assigns the next value read to the first slot in the array x belonging to an object called line (I'm assuming that line is an object you have instantiated and that x is a public field of that object...)

You want to increment an index and use that to address your arrays:

int i = 0;
while(input.hasNext())
{
    int num = input.nextInt(); // the first line integer
    line.x[i] = input.nextDouble(); //the additional line x coordinate
    line.y[i] = input.nextDouble(); //the additional line y coordinate
    i ++;

}

answered Oct 22, 2014 at 4:26

Jon Kiparsky

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