Java中BufferedReader的偶然错误

Question

I get an ArrayIndexOutOfBoundsException when I invoke this function, but not always. Out of 10 attempts , I got an error 3 times , and the remaining 7 times it worked perfectly fine.

void readTrainingData(Model m) throws FileNotFoundException  {

    BufferedReader br = null;

    try {
        br = new BufferedReader(new FileReader("training_data.csv"));
    } catch (IOException ex)    {
        throw new FileNotFoundException();
    }

    String line = "";
    int i = 0;
    int j;
    try {
        while((line = br.readLine()) != null)    {
            String[] coords = line.split(",");
            if (coords[0] != null && coords[1] != null) {
                m.x[i] = Float.parseFloat(coords[0]);
                m.y[i] = Float.parseFloat(coords[1]);
            }
            else    {
                System.out.println("Check training_data.csv");
            }

            j = 0;
            i++;
        }        
    } catch (IOException ex)    {
        System.out.println("Problem reading file");
        throw new RuntimeException(ex);
    }
}

The error is as follows :

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 1
    at polygonprobability.Util.readTrainingData(Util.java:215)

I can't debug it because whenever I'm trying to, I don't get the error.

I'm thoroughly confused. Please help.

EDIT : I changed the conditional to

if (coords[0] != null && coords[1] != null && coords.length == 2)   {
         m.x[i] = Float.parseFloat(coords[0]);
     m.y[i] = Float.parseFloat(coords[1]);
}

Line 215 happens to be the if conditional itself.

Even after the change, the error persists.

Answer 1

Do this changes

    if (coords.length == 2 && coords[0] != null && coords[1] != null )   {
             m.x[i] = Float.parseFloat(coords[0]);
         m.y[i] = Float.parseFloat(coords[1]);
    }

Answer 2

I get an Array IndexOutOfBoundsException when I invoke this function, but not always. Out of 10 attempts, I got an error 3 times, and the remaining 7 times it worked perfectly fine.

First potential danger :

if (coords[0] != null && coords[1] != null) 

Here you are assuming coords array will always have 2 elements .

Change your condition to :

 // check for coords.length == 2 first inside the if 
 // if the first condition fails , others won't be evaluated for short circuit AND
 if ( coords.length == 2 && coords[0] != null && coords[1] != null)   {
     m.x[i] = Float.parseFloat(coords[0]);
     m.y[i] = Float.parseFloat(coords[1]);
}

Second ,

m.x[i] = Float.parseFloat(coords[0]);
m.y[i] = Float.parseFloat(coords[1]);

Your x and y may not contain the index valued by i .

Show us your Model class , specifically the attributes x and y and how do you intialise them.

Answer 3

IndexOutOfBoundsException is thrown to indicate that an index of some sort (such as to an array, to a string, or to a vector) is out of range.

In your case i think following line of code is making problem,

 String[] coords = line.split(",");

you should check it's length coords.length before accessing it.

Answer 4

You're assuming that you will always have an array of at least two elements in coords , add some code to validate that you are indeed getting an array of at least two elements.

Change your if statement to:

if (coords.length >= 2) {
    m.x[i] = Float.parseFloat(coords[0]);
    m.y[i] = Float.parseFloat(coords[1]);
}

Answer 5

First check the length of the coords array then move forward as

if(coords.lenght()>=2) {
  //here parse your float
}

it is due to the unchecked length, you are assuming that coords length will be of 2 always.