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Roy
Asked: 2020-10-24 08:20:32 +0800 CST 2020-10-24 08:20:32 +0800 CST

How to limit the number of decimal places in a double?

  • 772

As the title says, I want to limit the number of decimals that result from an operation with variables of type double, this result is displayed in a JTextArea of ​​a JFrame.

The code that does the operation and prints the result in the JTextArea is as follows: ( la, lband lcrepresent the sides of a triangle, acalculates the area and Ais the JTextArea where the result is printed).

if (lb+lc>la && la+lc>lb && la+lb>lc){
     a=Math.sqrt((la+lb+lc)*(-la+lb+lc)*(la-lb+lc)*(la+lb-lc)/16);
     p=la+lb+lc;
     A.setText("El triangulo es "+t+".\nEl area es ("+a+").\nEl perimetro es ("+p+").");
java

5 Answers

  1. Best Answer

    There are many ways to limit the number of output decimal places (Presentation) of a double, but not the number itself, for example to double number = 1.4159999999;limit the output to 2 decimal places. if you want more digits it's a matter of adding zeros to String.format decimalformatand printf setScale BigDecimal`Round, cambiar el 2 por por la cantidad deseada enyY y ende

    1. Using DecimalFormat

       DecimalFormat df = new DecimalFormat("#.00");
 System.out.println(df.format(number));
 /* Salida : 1.42*/

    2. Using String.Format

      System.out.println(String.format("%.2f", number));
/* Salida : 1.42*/

    3. If you just want the output to have that format you would apply numberformat

      System.out.printf("Valor: %.2f", number ); 
/* Salida : 1.42*/

    4. Using Math.Round() where the number of zeros is the number of decimal places to limit

      System.out.println((double)Math.round(number * 100d) / 100d);
 /* Salida : 1.42*/

    5. Using the BigDecimal class , using the setScale method that receives two parameters: the number of decimal places to limit and the rounding mode

      BigDecimal bd = new BigDecimal(number);
bd = bd.setScale(2, RoundingMode.HALF_UP);
System.out.println(bd.doubleValue());
/* Salida 1.42*/
    • 32

  2. Try using String.format

    double valor = 123.456789;

String.format("%.3f", valor)  // 123.456

    You can combine everything like this, in this case it is a compact form that allows you to format everything together in a single line. 

    String.format("El triangulo es %s.\nEl area es (%.3f).\nEl perimetro es (%.3f).", t, a, p)

    Note that format automatically takes the locale setting, so depending on the country, you can use .or ,as a decimal separator.

    • 9

  3. You can use a DecimalFormat. For example:

    DecimalFormat formato = new DecimalFormat("#.000");

System.out.println(formato.format(p));

    It will return your value to three decimal places. You would have to add (or remove) as many zeros as decimals you want after the whole number.

    • 4

  4. The best I've found to reduce the number of decimal places in a double:

    number: the value with all decimals

    numberDecimals: how many decimals I want to retrieve

    Eg: 2.8049999999999997 returns 2.805

    double val = formatDecimals( 2.8049999999999997, 3);

    public static Double formatearDecimales(Double numero, Integer numeroDecimales) {
return Math.round(numero * Math.pow(10, numeroDecimales)) / Math.pow(10, numeroDecimales);
}
    • 2

  5. If you want to limit the number of unrounded decimals, you can do it like this:

    Double answer = 234.32545;
BigDecimal formatNumber = new BigDecimal(answer);
formatNumber = formatNumber.setScale(2, RoundingMode.DOWN);
System.out.println(formatNumber); // 234.32
    • 2