An example of comparing two double values with an epsilon.

DoubleEpsilonCompare.java

/**
     * Compare two {@code double} values
     * @param a some <i>double</i> value
     * @param b some other <i>double</i> value
     * @return {@code true} if the two values are equal
     */
    public static boolean equals (final double a, final double b) {
        if (a==b) return true;
        return Math.abs(a - b) < EPSILON; //EPSILON = 0.0000001d
    }

    /**
     * Compare {@code a} and {@code b}
     * @param a some <i>double</i> value
     * @param b some other <i>double</i> value
     * @return a negative value if {@code a} is smaller than {@code b},
     * a positive value if {@code a} is larger than {@code b}, else {code 0}.
     */
    public static int compare (final double a, final double b) {
        return equals(a, b) ? 0 : (a < b) ? -1 : +1;
    }

How do you define EPSILON? Is it a constant?

@chaoyangnz
Yes epsilon is a constant. See it as a error margin. If the two values are within EPSILON they are considered the same.
Example:
3.5 and 3.6 with EPSILON 0.05 are NOT considered EQUAL [abs(3.5-3.6) < 0.05]
3.5 and 3.6 with EPSILON 0.15 are considered EQUAL [abs(3.5-3.6) < 0.15]

2 years later you got a reply. Wohooo :D