为什么 BigDecimal 构造函数实例具有不同的值？
Why BigDecimal constructor instance with differents values?
我不知道为什么会这样：
float flo = 196.7f;
BigDecimal bd = new BigDecimal(flo);
System.out.println(bd); //print 196.6999969482421875
BigDecimal bd2 = new BigDecimal(Float.toString(flo));
System.out.println(bd2); //print 196.7
你的两个问题在 Javadoc 中都有明确说明。
- 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.
- 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.
我不知道为什么会这样：
float flo = 196.7f;
BigDecimal bd = new BigDecimal(flo);
System.out.println(bd); //print 196.6999969482421875
BigDecimal bd2 = new BigDecimal(Float.toString(flo));
System.out.println(bd2); //print 196.7
你的两个问题在 Javadoc 中都有明确说明。
- 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.
- 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.