java8-Double

 具体可以参考我写的这个文章。IEEE754浮点数规范。

注意此类里面的以下几点

有个神奇的语法。

System.out.println(0xfp3);

结果是120.0 0xf * 2 ^ 3

另外注意这俩个方法的区别

doubleToLongBits

doubleToRawLongBits

这俩个方法的区别在于对NAN的处理,doubleToLongBits对NAN返回的bit位符合IEEE754的规范。doubleToRawLongBits没有对NAN做任何的改变

另外，对NAN的任何结果都是NAN

public static void main(String[] args) throws NoSuchFieldException, SecurityException
    {
        check(Double.NEGATIVE_INFINITY);//-infinity
        check(Double.POSITIVE_INFINITY);//infinity
        check(Double.NaN);//NAN
        System.out.println(Double.NaN*Double.POSITIVE_INFINITY);//NaN
        System.out.println(Double.POSITIVE_INFINITY*1);//Infinity
        System.out.println(Double.NEGATIVE_INFINITY*1);//-Infinity
        System.out.println(Double.NEGATIVE_INFINITY*Double.POSITIVE_INFINITY);//-Infinity
        System.out.println(0xfp3);//120.0
        System.out.println(1e2);//100.0
    }

注意 compareTo的实现，先比较double，double比较还是相等(可能是精度区分不出来)，转成long比较。

 public static int compare(double d1, double d2) {
        if (d1 < d2)
            return -1;           // Neither val is NaN, thisVal is smaller
        if (d1 > d2)
            return 1;            // Neither val is NaN, thisVal is larger

        // Cannot use doubleToRawLongBits because of possibility of NaNs.
        long thisBits    = Double.doubleToLongBits(d1);
        long anotherBits = Double.doubleToLongBits(d2);

        return (thisBits == anotherBits ?  0 : // Values are equal
                (thisBits < anotherBits ? -1 : // (-0.0, 0.0) or (!NaN, NaN)
                 1));                          // (0.0, -0.0) or (NaN, !NaN)
    }