Getting wrong result for evaluation of 100 * 2.55 values

Question

I am getting wrong result using below method.

public double evaluate(final double leftOperand, final double rightOperand) {
        Double rtnValue = new Double(leftOperand * rightOperand);
        return rtnValue.doubleValue();
    }

Enter Parameter value are: leftOperand= 100 and rightOperand=2.55

I am getting Wrong answer: 254.99999999999997

The correct answer is a 255.0

Answer 1

This is due to floating point precision problem. It is impossible to represent every rational number within 64 bits. The numbers are stored within the IEEE 754 format.

If you are creating a game, this is more than good enough, even float will do. But if you are doing some finance, it should be correct. Then you can use java.math.BigDecimal. It is much slower than double but it is correct. And it takes much more memory, since you have an exact value in memory. Here is a nice tutorial on how to use BigDecimal.

Answer 2

Use BigDecimal

BigDecimal bd = new BigDecimal("100");
BigDecimal ans = bd.multiple(new BigDecimal("2.55"));
System.out.println(ans);

See Also

• Working IDE One demo

• Retain precision with double in Java

Answer 3

Using Math.round().

public static double evaluate(final double leftOperand, final double rightOperand) {
        Double rtnValue = new Double(leftOperand * rightOperand);
        return Math.round(rtnValue.doubleValue());
    }