JAVA Math floor() round()

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floor（不大于他的最大整数

    /**     * Returns the double conversion of the most positive (closest to positive     * infinity) integer value which is less than the argument.     * <p>     * Special cases:     * <ul>     * <li>{@code floor(+0.0) = +0.0}</li>     * <li>{@code floor(-0.0) = -0.0}</li>     * <li>{@code floor(+infinity) = +infinity}</li>     * <li>{@code floor(-infinity) = -infinity}</li>     * <li>{@code floor(NaN) = NaN}</li>     * </ul>     *     * @param d     *            the value whose closest integer value has to be computed.     * @return the floor of the argument.     */    public static native double floor(double d);

round（四舍五入

    /**     * Returns the result of rounding the argument to an integer. The result is     * equivalent to {@code (long) Math.floor(d+0.5)}.     * <p>     * Special cases:     * <ul>     * <li>{@code round(+0.0) = +0.0}</li>     * <li>{@code round(-0.0) = +0.0}</li>     * <li>{@code round((anything > Long.MAX_VALUE) = Long.MAX_VALUE}</li>     * <li>{@code round((anything < Long.MIN_VALUE) = Long.MIN_VALUE}</li>     * <li>{@code round(+infinity) = Long.MAX_VALUE}</li>     * <li>{@code round(-infinity) = Long.MIN_VALUE}</li>     * <li>{@code round(NaN) = +0.0}</li>     * </ul>     *     * @param d     *            the value to be rounded.     * @return the closest integer to the argument.     */    public static long round(double d) {        // check for NaN        if (d != d) {            return 0L;        }        return (long) floor(d + 0.5d);    }

round(float t)

/**     * Returns the result of rounding the argument to an integer. The result is     * equivalent to {@code (int) Math.floor(f+0.5)}.     * <p>     * Special cases:     * <ul>     * <li>{@code round(+0.0) = +0.0}</li>     * <li>{@code round(-0.0) = +0.0}</li>     * <li>{@code round((anything > Integer.MAX_VALUE) = Integer.MAX_VALUE}</li>     * <li>{@code round((anything < Integer.MIN_VALUE) = Integer.MIN_VALUE}</li>     * <li>{@code round(+infinity) = Integer.MAX_VALUE}</li>     * <li>{@code round(-infinity) = Integer.MIN_VALUE}</li>     * <li>{@code round(NaN) = +0.0}</li>     * </ul>     *     * @param f     *            the value to be rounded.     * @return the closest integer to the argument.     */    public static int round(float f) {        // check for NaN        if (f != f) {            return 0;        }        return (int) floor(f + 0.5f);    }

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