Double d = 13.3D;

BigDecimal bd1 = new BigDecimal(d);
BigDecimal bd2 = new BigDecimal(String.valueOf(d));


System.out.println("RESULT 1: "+bd1.toString());
System.out.println("RESULT 2: "+bd2.toString());

RESULT 1: 13.300000000000000710542735760100185871124267578125
RESULT 2: 13.3

那么，API在构造函数BigDecimal(double val)中解决了这个明显的不一致：

1. The results of this constructor can be somewhat unpredictable. One might
   assume that writing new
   BigDecimal(0.1) in Java creates a
   BigDecimal which is exactly equal to
   0.1 (an unscaled value of 1, with a scale of 1), but it is actually equal
   to
   0.1000000000000000055511151231257827021181583404541015625. This is because 0.1 cannot be
   represented exactly as a double (or,
   for that matter, as a binary fraction
   of any finite length). Thus, the value
   that is being passed in to the
   constructor is not exactly equal to
   0.1, appearances notwithstanding.

2. The String constructor, on the other hand, is perfectly predictable:
   writing new BigDecimal(“0.1”) creates
   a BigDecimal which is exactly equal to
   0.1, as one would expect. Therefore, it is generally recommended that the
   String constructor be used in
   preference to this one.

3. When a double must be used as a source for a BigDecimal, note that
   this constructor provides an exact
   conversion; it does not give the same
   result as converting the double to a
   String using the
   Double.toString(double) method and
   then using the BigDecimal(String)
   constructor. To get that result, use
   the static valueOf(double) method.

道德的故事：痛苦似乎是自我造成的，只是使用new BigDecimal(String val)或BigDecimal.valueOf(double val)代替=)