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Kiwi is a utility library. We really like Google's Guava, and also use Apache Commons. But if they don't have something we need, and we think it is useful, this is where we put it.
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package org.kiwiproject.base;

import com.google.common.math.DoubleMath;
import lombok.experimental.UtilityClass;

/**
 * {@link Double} utilities. Mainly wrappers around existing method in {@link Double} and {@link DoubleMath} that
 * are (in our opinion anyway) easier to work with or read the code, e.g. return a boolean for comparisons instead
 * of an int.
 */
@UtilityClass
public class KiwiDoubles {

    /**
     * Default tolerance to use for comparisons when not explicitly specified.
     */
    public static final double DEFAULT_FUZZY_EQUALS_TOLERANCE = 1E-9;

    /**
     * Return true if value is exactly equal to zero.
     *
     * @param value the value to check
     * @return true if the value is zero
     * @see Double#compare(double, double)
     */
    public static boolean isZero(double value) {
        return areEqual(value, 0.0);
    }

    /**
     * Return true if value is not exactly equal to zero.
     *
     * @param value the value to check
     * @return true if the value is not zero
     * @see Double#compare(double, double)
     */
    public static boolean isNotZero(double value) {
        return areNotEqual(value, 0.0);
    }

    /**
     * Return true if value is close to zero, within the default tolerance.
     *
     * @param value the value to check
     * @return true if the value is close to zero using the {@link #DEFAULT_FUZZY_EQUALS_TOLERANCE}
     * @see DoubleMath#fuzzyEquals(double, double, double)
     * @see #DEFAULT_FUZZY_EQUALS_TOLERANCE
     */
    public static boolean isCloseToZero(double value) {
        return isCloseToZero(value, DEFAULT_FUZZY_EQUALS_TOLERANCE);
    }

    /**
     * Return true if value is close to zero, using the given tolerance.
     *
     * @param value     the value to check
     * @param tolerance how far away the value can be from zero while still considered equal to zero
     * @return true if the value is close to zero
     * @see DoubleMath#fuzzyEquals(double, double, double)
     */
    public static boolean isCloseToZero(double value, double tolerance) {
        return DoubleMath.fuzzyEquals(value, 0.0, tolerance);
    }

    /**
     * Return true if value1 is numerically equal to value2.
     *
     * @param value1 the first value to compare
     * @param value2 the second value to compare
     * @return true if value1 equals value2
     * @see Double#compare(double, double)
     */
    public static boolean areEqual(double value1, double value2) {
        return Double.compare(value1, value2) == 0;
    }

    /**
     * Return true if value1 is not numerically equal to value2.
     *
     * @param value1 the first value to compare
     * @param value2 the second value to compare
     * @return true if value1 does not equal value2
     * @see Double#compare(double, double)
     */
    public static boolean areNotEqual(double value1, double value2) {
        return !areEqual(value1, value2);
    }

    /**
     * Return true if value1 is close to value2, within the default tolerance.
     *
     * @param value1 the first value to compare
     * @param value2 the second value to compare
     * @return true if value1 is close to value2 using the {@link #DEFAULT_FUZZY_EQUALS_TOLERANCE}
     * @see DoubleMath#fuzzyEquals(double, double, double)
     * @see #DEFAULT_FUZZY_EQUALS_TOLERANCE
     */
    public static boolean areClose(double value1, double value2) {
        return areClose(value1, value2, DEFAULT_FUZZY_EQUALS_TOLERANCE);
    }

    /**
     * Return true if value1 is close to value2, within the given tolerance.
     *
     * @param value1    the first value to compare
     * @param value2    the second value to compare
     * @param tolerance how far away the values can be from each other while still considered equal
     * @return true if value1 is close to value2 using the {@link #DEFAULT_FUZZY_EQUALS_TOLERANCE}
     * @see DoubleMath#fuzzyEquals(double, double, double)
     */
    public static boolean areClose(double value1, double value2, double tolerance) {
        return DoubleMath.fuzzyEquals(value1, value2, tolerance);
    }
}