Convert string to BigDecimal in java

Question

I am reading a currency from XML into Java.

String currency = "135.69"; 

When I convert this to BigDecimal I get:

 System.out.println(new BigDecimal(135.69)); 

Output:

135.68999999999999772626324556767940521240234375. 

Why is it that it outputs this many numbers? How can I avoid this? All I want is for it to output 135.69.

Answer 1

The BigDecimal(double) constructor can have unpredictable behaviors. It is preferable to use BigDecimal(String) or BigDecimal.valueOf(double).

System.out.println(new BigDecimal(135.69)); //135.68999999999999772626324556767940521240234375 System.out.println(new BigDecimal("135.69")); // 135.69 System.out.println(BigDecimal.valueOf(135.69)); // 135.69 

The documentation for BigDecimal(double) explains in detail:

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.