import java.text.DecimalFormat;

public class DecimalFormatExample {

    public static void main(String[] args) {

        double number = 123.456;

        //15 digits after decimal point
        DecimalFormat decimalFormat = new DecimalFormat(".000000000000000");
        System.out.println(decimalFormat.format(number));

        //15 digits before and after decimal point
        DecimalFormat decimalFormat2 = new DecimalFormat("000000000000000.000000000000000");
        System.out.println(decimalFormat2.format(number));

        //15 digits after decimal point
        System.out.printf("%.15f", number);
    }
}