Scientific notation to decimal

问题

I have a double and i am trying to convert it to a decimal. When i use decimalformat to achieve this i get the following:

public void roundNumber(){
    double d = 2.081641999208976E-4;
    JOptionPane.showMessageDialog(null,roundFiveDecimals(d));
}

public double roundFiveDecimals(double d) {
    DecimalFormat df = new DecimalFormat("#.#####");
    return Double.valueOf(df.format(d));
}

I want the output to be .00021; however, i get 2.1E-4. Can anyone help explain how to get .00021 and not 2.1E-4?

回答1:

You're parsing the result from DecimalFormat - you should be returning it as a String:

public String roundFiveDecimals(double d) {
    DecimalFormat df = new DecimalFormat("#.#####");
    return df.format(d);
}

The double value itself has no concept of formatting - it's just a number. It's the job of DecimalFormat to format the value into text however you want... if you then convert that text back into a number, you've lost that work.

来源：https://stackoverflow.com/questions/6878623/scientific-notation-to-decimal