Format double value in scientific notation

问题:

I have a double number like 223.45654543434 and I need to show it like 0.223x10e+2.

How can I do this in Java?

回答1:

    System.out.println(String.format("%6.3e",223.45654543434));

results in

    2.235e+02

which is the closest I get.

more info : http://java.sun.com/j2se/1.5.0/docs/api/java/util/Formatter.html#syntax

回答2:

From Display numbers in scientific notation. (Copy/pasting because the page seems to be having issues)

---

You can display numbers in scientific notation using java.text package. Specifically DecimalFormat class in java.text package can be used for this aim.

The following example shows how to do this:

import java.text.*;
import java.math.*;

public class TestScientific {

  public static void main(String args[]) {
     new TestScientific().doit();
  }

  public void doit() {
     NumberFormat formatter = new DecimalFormat();

     int maxinteger = Integer.MAX_VALUE;
     System.out.println(maxinteger);    // 2147483647

     formatter = new DecimalFormat("0.######E0");
     System.out.println(formatter.format(maxinteger)); // 2,147484E9

     formatter = new DecimalFormat("0.#####E0");
     System.out.println(formatter.format(maxinteger)); // 2.14748E9


     int mininteger = Integer.MIN_VALUE;
     System.out.println(mininteger);    // -2147483648

     formatter = new DecimalFormat("0.######E0");
     System.out.println(formatter.format(mininteger)); // -2.147484E9

     formatter = new DecimalFormat("0.#####E0");
     System.out.println(formatter.format(mininteger)); // -2.14748E9

     double d = 0.12345;
     formatter = new DecimalFormat("0.#####E0");
     System.out.println(formatter.format(d)); // 1.2345E-1

     formatter = new DecimalFormat("000000E0");
     System.out.println(formatter.format(d)); // 12345E-6
  }
}  

回答3:

This answer will save time for the 40k+ people who are googling "java scientific notation."

What does Y mean in %X.YE?

The number between the . and E is the number of decimal places (NOT the significant figures).

System.out.println(String.format("%.3E",223.45654543434));
// "2.235E+02"
// rounded to 3 decimal places, 4 total significant figures

The String.format method requires you to specify the number of decimal digits to round to. If you need to preserve the exact significance of the original number then you will need a different solution.

What does X mean in %X.YE?

The number between the % and . is the minimum number of characters the string will take up. (this number is not necessary, as shown above the the string will automatically fill if you leave it out)

System.out.println(String.format("%3.3E",223.45654543434));
// "2.235E+02" <---- 9 total characters
System.out.println(String.format("%9.3E",223.45654543434));
// "2.235E+02" <---- 9 total characters
System.out.println(String.format("%12.3E",223.45654543434));
// "   2.235E+02" <---- 12 total characters, 3 spaces
System.out.println(String.format("%12.8E",223.45654543434));
// "2.23456545E+02" <---- 14 total characters
System.out.println(String.format("%16.8E",223.45654543434));
// "  2.23456545E+02"  <---- 16 total characters, 2 spaces

回答4:

Finally I do it by hand:

public static String parseToCientificNotation(double value) {
        int cont = 0;
        java.text.DecimalFormat DECIMAL_FORMATER = new java.text.DecimalFormat("0.##");
        while (((int) value) != 0) {
            value /= 10;
            cont++;
        }
        return DECIMAL_FORMATER.format(value).replace(",", ".") + " x10^ -" + cont;
}