Java字符串解析错误

Question

Hey can someone help me with my error i am getting. I am taking apart lines out of my file and check wether they are low med or high. If the string is blank i want to read the next line in the file. I think the error is when i am parsing the sting to a double. Heres my code any help is appriciated! First here is my error

Exception in thread "main" java.lang.NumberFormatException: empty String
    at sun.misc.FloatingDecimal.readJavaFormatString(Unknown Source)
    at java.lang.Double.parseDouble(Unknown Source)
    at BSCQueryManager.displayBar(BSCQueryManager.java:431)
    at BSCQueryManager.main(BSCQueryManager.java:57)

Here is my code

String vMag;
            String data;
            double v;
            int highCount = 0;
            int medCount = 0;
            int lowCount = 0;
            // read file
            File inFile = new File("bsc.dat");   
            Scanner starFile = new Scanner(inFile);
            // while there is a vmag
            while(starFile.hasNext()){
                // read next line
                data = starFile.nextLine();
                data = data.substring(102, 107);
                data.trim();
            // if no vmag read next line
                if(data.trim()!= ""){
                    v = Double.parseDouble(data);
                    // if vmag is > 6.0 add to countHigh
                    if (v > 6){
                        highCount++;
                    }
                    // if vmag is 5-6 add to countMed
                    if (v >= 5 && v <= 6){
                        medCount++;
                    }
                    // if vmag is < 5 add to countLow
                    if (v < 5){
                        lowCount++;
                    }
                // end if
                }
            // end while
            }

            // display label
            System.out.println(label);
            System.out.println(highCount);
            System.out.println(lowCount);
            System.out.println(medCount);

Answer 1

Try replacing:

data.trim();
// if no vmag read next line
if(data.trim()!= ""){

with

data = data.trim();
// if no vmag read next line
if(data.length > 0){

Answer 2

One of the strings is empty:

class Test1 {
    public static void main(String[] args) {
        Double.parseDouble("");
    }
}

produces:

C:\Temp>java Test1
Exception in thread "main" java.lang.NumberFormatException: empty String
        at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:992)
        at java.lang.Double.parseDouble(Double.java:510)
        at Test1.main(Test1.java:3)

Answer 3

The data string definitely isn't parsable to a double. It may be blank (your string not empty logic is flawed, try

data.isEmpty() 

instead) or the value could be something else unparseable eg a letter or word.

You could try debugging, or catching the exception and printing the value of data.

try{
 Double.parseDouble(data);
}catch(NumberFormatException e){
throw new RuntimeException(data + " is not a number");
}

That will let you see what's going wrong.