How to limit the number of decimals of a double?


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

The code that does the operation and prints the result in the JTextArea is the following: ( la , lb and lc represent the sides of a triangle, a calculate the area and A is the JTextArea where the result is printed).

if (lb+lc>la && la+lc>lb && la+lb>lc){
     A.setText("El triangulo es "+t+".\nEl area es ("+a+").\nEl perimetro es ("+p+").");
asked by Roy 23.10.2016 в 18:20

5 answers


There are many ways to limit the number of decimals of output (Presentation) of a double , but not the number itself, for example for double number = 1.4159999999; limit the output to 2 decimals. if you want more digits it is a matter of adding zeros in decimalformat and Round, cambiar el 2 por por la cantidad deseada en String.format y printf Y y en setScale de BigDecimal '

  • Using DecimalFormat

     DecimalFormat df = new DecimalFormat("#.00");
     /* Salida : 1.42*/
  • Using String.Format

    System.out.println(String.format("%.2f", number));
    /* Salida : 1.42*/
  • If you only want the output to have that format, you would apply numberformat

    System.out.printf("Valor: %.2f", number ); 
    /* Salida : 1.42*/
  • 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*/
  • Using the class BigDecimal , using the setScale that receives two parameters the number of decimals limit and rounding mode

    BigDecimal bd = new BigDecimal(number);
    bd = bd.setScale(2, RoundingMode.HALF_UP);
    /* Salida 1.42*/
  • answered by 23.10.2016 / 18:35

    Test using String.format

    double valor = 123.456789;
    String.format("%.3f", valor)  // 123.456

    You can combine everything like that, for this case it is a compact form and it 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 configuration, so depending on the country, you can use . or , as a decimal point separator.

    answered by 23.10.2016 в 18:35

    You can use a DecimalFormat . For example:

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

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

    answered by 23.10.2016 в 18:36

    The best thing I've found to reduce the number of decimals of a double:

    number: the value with all the decimals

    NumberDecimals: how many decimals do I want to recover?

    Ahem: 2.8049999999999997 returns 2,805

    double val = formattingDecimals (2.8049999999999997, 3);

    public static Double formatearDecimales(Double numero, Integer numeroDecimales) {
    return Math.round(numero * Math.pow(10, numeroDecimales)) / Math.pow(10, numeroDecimales);
    answered by 02.05.2018 в 19:24

    If you want to limit the number of decimals without rounding, you can do it in the following way:

    Double answer = 234.32545;
    BigDecimal formatNumber = new BigDecimal(answer);
    formatNumber = formatNumber.setScale(2, RoundingMode.DOWN);
    System.out.println(formatNumber); // 234.32
    answered by 01.08.2018 в 09:03