Getting Rounding errors in Bigdecimal for RoundingModes - HALF_UP/EVEN in JRE 7/8/11

Question

When I try the below code I am getting 2 strange outputs

42.01 42.01

82.00 82.00

Is anyone sure about why this is happening ? and can it be resolved with the using the below RoundingMode for BigDecimal in java 7/8.

import java.math.*;
class HelloWorld {
    public static void main(String[] args) {
    
      BigDecimal hup = new BigDecimal(42.0050).setScale(2,
                                            RoundingMode.HALF_UP);
      BigDecimal hev = new BigDecimal(42.0050).setScale(2,
                                        RoundingMode.HALF_EVEN);                                    
        
      BigDecimal hup2 = new BigDecimal(82.0050).setScale(2,
                                            RoundingMode.HALF_UP);
      BigDecimal hev2 = new BigDecimal(82.0050).setScale(2,
                                        RoundingMode.HALF_EVEN);
     
     
       System.out.println(hup);
       System.out.println(hev);
       System.out.println(hup2);
       System.out.println(hev2);
}}

Thanks.

user_496038 · Answer

That's a funny question.

Change your input to this and see the difference:

BigDecimal hup = new BigDecimal("42.0050").setScale(2,
    RoundingMode.HALF_UP);
BigDecimal hev = new BigDecimal("42.0050").setScale(2,
    RoundingMode.HALF_EVEN);

The result will be:

42.01 42.00

The problem, in reality, is how the input to BigDecimal is given.

In IntelliJ, for example, you see a warning when using BigDecimal not as String:

Getting Rounding errors in Bigdecimal for RoundingModes - HALF_UP/EVEN in JRE 7/8/11

1 Answers