I need to convert String value to float at java [duplicate]
I want to print a double value in Java without exponential form.
double dexp = 12345678;
System.out.println("dexp: "+dexp);
It shows this E notation: 1.2345678E7
.
I want it to print it like this: 12345678
What is the best way to prevent this?
Java prevent E notation in a double:
Five different ways to convert a double to a normal number:
import java.math.BigDecimal;
import java.text.DecimalFormat;
public class Runner {
public static void main(String[] args) {
double myvalue = 0.00000021d;
//Option 1 Print bare double.
System.out.println(myvalue);
//Option2, use decimalFormat.
DecimalFormat df = new DecimalFormat("#");
df.setMaximumFractionDigits(8);
System.out.println(df.format(myvalue));
//Option 3, use printf.
System.out.printf("%.9f", myvalue);
System.out.println();
//Option 4, convert toBigDecimal and ask for toPlainString().
System.out.print(new BigDecimal(myvalue).toPlainString());
System.out.println();
//Option 5, String.format
System.out.println(String.format("%.12f", myvalue));
}
}
This program prints:
2.1E-7
.00000021
0.000000210
0.000000210000000000000001085015324114868562332958390470594167709350585
0.000000210000
Which are all the same value.
Protip: If you are confused as to why those random digits appear beyond a certain threshold in the double value, this video explains: computerphile why does 0.1
+0.2
equal 0.30000000000001
?
http://youtube.com/watch?v=PZRI1IfStY0
You could use printf()
with %f
:
double dexp = 12345678;
System.out.printf("dexp: %f\n", dexp);
This will print dexp: 12345678.000000
. If you don't want the fractional part, use
System.out.printf("dexp: %.0f\n", dexp);
0 in %.0f
means 0 places in fractional part i.e no fractional part. If you want to print fractional part with desired number of decimal places then instead of 0 just provide the number like this %.8f
. By default fractional part is printed up to 6 decimal places.
This uses the format specifier language explained in the documentation.
The default toString()
format used in your original code is spelled out here.
In short:
If you want to get rid of trailing zeros and Locale problems, then you should use:
double myValue = 0.00000021d;
DecimalFormat df = new DecimalFormat("0", DecimalFormatSymbols.getInstance(Locale.ENGLISH));
df.setMaximumFractionDigits(340); // 340 = DecimalFormat.DOUBLE_FRACTION_DIGITS
System.out.println(df.format(myValue)); // Output: 0.00000021
Explanation:
Why other answers did not suit me:
-
Double.toString()
orSystem.out.println
orFloatingDecimal.toJavaFormatString
uses scientific notations if double is less than 10^-3 or greater than or equal to 10^7 -
By using
%f
, the default decimal precision is 6, otherwise you can hardcode it, but it results in extra zeros added if you have fewer decimals. Example:double myValue = 0.00000021d; String.format("%.12f", myvalue); // Output: 0.000000210000
-
By using
setMaximumFractionDigits(0);
or%.0f
you remove any decimal precision, which is fine for integers/longs, but not for double:double myValue = 0.00000021d; System.out.println(String.format("%.0f", myvalue)); // Output: 0 DecimalFormat df = new DecimalFormat("0"); System.out.println(df.format(myValue)); // Output: 0
-
By using DecimalFormat, you are local dependent. In French locale, the decimal separator is a comma, not a point:
double myValue = 0.00000021d; DecimalFormat df = new DecimalFormat("0"); df.setMaximumFractionDigits(340); System.out.println(df.format(myvalue)); // Output: 0,00000021
Using the ENGLISH locale makes sure you get a point for decimal separator, wherever your program will run.
Why using 340 then for setMaximumFractionDigits
?
Two reasons:
-
setMaximumFractionDigits
accepts an integer, but its implementation has a maximum digits allowed ofDecimalFormat.DOUBLE_FRACTION_DIGITS
which equals 340 -
Double.MIN_VALUE = 4.9E-324
so with 340 digits you are sure not to round your double and lose precision.
You can try it with DecimalFormat
. With this class you are very flexible in parsing your numbers.
You can exactly set the pattern you want to use.
In your case for example:
double test = 12345678;
DecimalFormat df = new DecimalFormat("#");
df.setMaximumFractionDigits(0);
System.out.println(df.format(test)); //12345678