double相乘少一分的问题，BigDecimal参数传小数也会出问题

public static void main(String[] args) {
    System.out.println(String.valueOf((int) (19.9 * 100))); //1989
　　 double aa = 19.9;
    double bb = 100;
    System.out.println(aa*bb); //1989.9999999999998
    BigDecimal v1 = new BigDecimal("19.9");
    BigDecimal v2 = new BigDecimal("100");
    Double v = v1.multiply(v2).doubleValue();
　　System.out.println(v.intValue()); //1990
    System.out.println(v); //1990.0

    BigDecimal b1 = new BigDecimal(19.9);
    BigDecimal b2 = new BigDecimal(100);
    System.out.println(b1);  //19.89999999999999857891452847979962825775146484375
    Double b = b1.multiply(b2).doubleValue();
    System.out.println(b.intValue()); //1989
    System.out.println(b); //1989.9999999999998
}

结论就是小数相乘，要使用BigDecimal且构造参数传入字符串