将字符串解析为Double时，数字格式异常

Question

I'm running into a problem of reading from a text file off a web server, and parsing that string to a Double to use for subsequent things. This is a sample line from the web server I'm reading from.

Sample line:

"00501","+40.922326","-072.637078","HOLTSVILLE","NY","SUFFOLK","UNIQUE"

-Data is separated by commas so I'm using a delimiter for that.

And this is how I'm trying to parse the double values:

 String latitude = scan.next();
 tempLatitude = Double.parseDouble(latitude);
 String longitude = scan.next();
 tempLongitude = Double.parseDouble(longitude);

And I have a catch for Number Format Exception to print the message and I get:

For input string: ""+40.922326""

And the error message(without the catch for NFE):

Exception in thread "main" java.lang.NumberFormatException: For input string: ""+40.922326""
at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1224)
at java.lang.Double.parseDouble(Double.java:510)
at Processor.readData(Processor.java:44)
at Application.main(Application.java:12)

Processor is the class all this stuff is in. Application invokes it through an object the void method readData and I have another class that stores the variables into arrays of that type.

Let me know if you need to see more code! Thanks.

Answer 1

As you can see "+40.922326" has double quotes arround the number. And that can not be parsed. you have to remove the quotes bevor you parse the number.

Answer 2

You need to remove the quotes at the start and the end of the numbers. You can write a simple method to do that:

private double parseDouble(String string) {
    if(string.startsWith("\"")) {
        string = string.substring(1);
    }
    if(string.endsWith("\"")) {
        string = string.substring(0, string.length()-1);
    }
    return Double.parseDouble(string);
}

You can also rely on regular expressions to parse the value wrapped in quotes:

private double parseDouble(String string) {
    Pattern pattern = Pattern.compile("\"?([+\\-]?\\d+(\\.\\d+)?)\"?");
    Matcher matcher = pattern.matcher(string);
    if (matcher.find()) {
        return Double.parseDouble(matcher.group(1));
    }
    return 0;
}

System.out.println(parseDouble("\"+40.922326\""));  // prints 40.922326
System.out.println(parseDouble("\"-40.922326\""));  // prints -40.922326

Answer 3

您也可以使用substring（）方法删除双引号。

tempLatitude = Double.parseDouble(latitude.substring(1,latitude.length()-1);