Read long integers from txt in java

Question

I have a list of long integers in a text file. I want to read those numbers to long arraylist in java. Out numbers are stored in the file:

2.2278e+08
1.2339e+09
6.1868e+08

My code to read those long numbers are the following:

for (String line : Files.readAllLines(Paths.get("ids.txt"))) {
                    ids.add(Long.parseLong(line, 10));
                    System.out.println(Double.valueOf(line).longValue());
}

However I got the following exceptions:

Exception in thread "main" java.lang.NumberFormatException: For input string: "2.2278e+08"
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
at java.lang.Long.parseLong(Long.java:589)
at twittertrendsetters.TwitterTrendSetters.main(TwitterTrendSetters.java:580)

Java Result: 1

How can I convert 2.2278e+08 to the long integer number 22278111 which is in fact

The number is stored in floating-point format. You may want to use `Double.valueOf(line)` instead. Then you can turn it into a long if you want doing `Double.longValue()` instance method. — Edwin Dalorzo, Jan 29 '15 at 12:48
This is called scientific notation. You may want to look here: http://stackoverflow.com/questions/2722122/java-parse-a-number-in-exponential-notation — Zhedar, Jan 29 '15 at 12:49
System.out.println(Double.valueOf(line)); gives me the same error. — Jose Ramon, Jan 29 '15 at 12:49
@EdwinDalorzo +1 - you should answer instead of commenting in this case. — Mena, Jan 29 '15 at 12:49
@Sarvesh `parseDouble` returns a primitive double, therefore it is not an object and you cannot dereference it. — Edwin Dalorzo, Jan 29 '15 at 12:54
@EdwinDalorzo You are right. I was using scala console, and forgot that part because of implicit conversion to object by Scala. — sarveshseri, Jan 29 '15 at 13:00

score 2 · Accepted Answer · answered Jan 29 '15 at 12:53

The thing is that numbers like 2.2278e+08, 1.2339e+09 and 6.1868e+08 are in floating-point notation and therefore cannot be parsed as long numbers directly.

However you could parse them as double values doing something like

long l = Double.valueOf("2.2278e+08").longValue();

Of course this departs from the assumption that you know that all these numbers are integers and that they fit in the size of a long value. Otherwise you may need to resort to other techniques.

As a side note, `new BigDecimal("2.2278e+08").longValue()` would also work, but the result should be the same. — Tom, Jan 29 '15 at 12:56

Read long integers from txt in java

1 Answers1