Java Fraction Format formatNumber(double value, double epsilon)

Description

Formats a number so that it presents a number of significant figures corresponding to a supplied small difference.

License

LGPL

Parameter

Parameter	Description
value	value to format
epsilon	small value

Return

formatted value

Declaration

public static String formatNumber(double value, double epsilon) 

Method Source Code

//package com.java2s;
//License from project: LGPL 

import java.text.DecimalFormat;

public class Main {
    /**/* www. j a va  2 s .  c om*/
     * Numeric formatting utility function.
     *
     * @param  value  numeric value to format
     * @param  baseFmt  format string as for {@link java.text.DecimalFormat}
     * @param  nFracDigits  fixed number of digits after the decimal point
     * @return  formatted string
     */
    public static String formatNumber(double value, String baseFmt, int nFracDigits) {
        DecimalFormat fmt = new DecimalFormat(baseFmt);
        fmt.setMaximumFractionDigits(nFracDigits);
        fmt.setMinimumFractionDigits(nFracDigits);
        return fmt.format(value);
    }

    /**
     * Formats a number so that it presents a number of significant figures
     * corresponding to a supplied small difference.
     * The idea is that the output should be compact, but that applying
     * this function to value and value+epsilon should give visibly
     * different results.  The number of significant figures is determined
     * by epsilon, not further rounded (trailing zeroes are not truncated).
     *
     * @param   value   value to format
     * @param   epsilon   small value
     * @return  formatted value
     */
    public static String formatNumber(double value, double epsilon) {
        epsilon = Math.abs(epsilon);

        /* Work out the number of significant figures. */
        double aval = Math.abs(value);
        int nsf = Math.max(0, (int) Math.round(-Math.log10(epsilon / aval)));

        /* Return a formatted string on this basis. */
        if (aval >= 1e6 || aval <= 1e-4) {
            return formatNumber(value, "0.#E0", nsf);
        } else if (epsilon >= 0.9) {
            return Long.toString((long) Math.round(value));
        } else {
            int ndp = (int) Math.round(Math.max(0, -Math.log10(epsilon)));
            return ndp == 0 ? Long.toString((long) Math.round(value)) : formatNumber(value, "0.0", ndp);
        }
    }
}

Related

1. formatNumber(Double number, String pattern)
2. formatNumber(Double numberToFormat, int decimalPlacement)
3. formatNumber(double paramDouble, int paramInt)
4. formatNumber(double pValue)
5. formatNumber(double value)
6. formatNumber(final double number)
7. formatNumber(Float d, int scalar)
8. formatNumber(float num, String format)
9. formatNumber(int fractionDigits, double value)