Q:

Long float-number output shows letters

I have the following code:
String curDir = ".";
File fileObject = new File(curDir);
File[] fileList = fileObject.listFiles();

float fileLengthMegabytes = (float)fileList[i].length() / 1000000;

The method fileList[i].length() returns 311 bytes as the type Long.
The previous code results in the following output:
3.88E-4
How do I get my expected output of 0,000311 inside the fileLengthMegabytes variable?

A:

That is Scientific Notation.
AND you are getting 388 instead of 311 because you are dividing by 1000000 instead of 1048576 (1024 * 1024)
EDIT: 311 is not achieved even with 1048576, that way you get 370... so the error is probably in your calc ;)
As described here , you just have to convert your Scientific Notation to a Decimal Notation through a Formatter.
DecimalFormat df = new DecimalFormat("#.########");
return df.format(fileLengthMegabytes);

Running Example: http://ideone.com/2lkKv7
import java.util.*;
import java.lang.*;
import java.text.*;

class Main
{
    public static void main (String[] args) throws java.lang.Exception
    {
                DecimalFormat df = new DecimalFormat("#.##########");

        float fileLengthMegabytes1 = (float) 388 / 1000000;
        float fileLengthMegabytes2 = (float) 388 / 1048576;
        System.out.println("MB1 in Scientific Notation: " + 
                            fileLengthMegabytes1);        
        System.out.println("MB1 in Decimal Notation: " + 
                            df.format(fileLengthMegabytes1));
        System.out.println("MB2 in Scientific Notation: " + 
                            fileLengthMegabytes2);        
        System.out.println("MB2 in Decimal Notation: " + 
                            df.format(fileLengthMegabytes2));
        }
}

Output:

MB1 in Scientific Notation: 3.88E-4
MB1 in Decimal Notation: 0.000388
MB2 in Scientific Notation: 3.7002563E-4
MB2 in Decimal Notation: 0.0003700256

A:

This is the way Java(and many other languages) display floating point numbers. E just means 10^, so 3.88E-4 is another way of writing 3.88 x 10^-4, which is the same as 0.000388.
This format is called scientific notation. E-notation is a computer representation of scientific notation.
The rest of your inaccuracy (388 vs 311) is because 1000000 is not the exact number you want to be dividing by. See the other answers for more details.

