Java BigDecimal operation: How to accurately control the accuracy of calculation results?

Java BigDecimal operation: How to accurately control the accuracy of calculation results?

In Java programming, the BigDecimal class is often used for high-precision calculations, but sometimes the calculation results do not match expectations. For example:

 public static void main(String[] args) {
    BigDecimal currentInventoryNumber = BigDecimal.valueOf(872.000);
    BigDecimal convertedNumber = BigDecimal.valueOf(0.200);
    System.out.println(currentInventoryNumber.subtract(convertedNumber, new MathContext(3)));
}

This code outputs 872, rather than the expected 871.800. This is because MathContext(3) limits the result accuracy to 3 significant digits, resulting in the decimal part being rounded.

MathContext class controls the accuracy and rounding mode of BigDecimal operations. new MathContext(3) specifies the precision of 3, which means the result will be rounded to three decimal places. Since the third decimal point of 871.800 is 0, which is less than 5, the result is rounded to 872.000. The tail zero is omitted when BigDecimal outputs, and finally it is displayed as 872.

To obtain more accurate results, you need to adjust the MathContext parameter or directly use the subtract() method without MathContext parameter to preserve all decimal places. This emphasizes that when using BigDecimal for calculations, the impact of precision and rounding mode on the results must be carefully considered. Selecting the right MathContext or avoiding it will ensure the accuracy of the calculation results.

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