Adding 2 doubles together yields incorrect results

Question

I have a problem with adding 2 doubles to produce a running total where it appears to also add 0.0000000000000(1 to 9).
The code illustrates my problem and is causing a big issue, I have found references to fix this which use BigDecimal but I want to now what is going wrong.
public class Test1
public static void main(String args[])
String strValue = "";
double dTotal = 0;
double dTotalOLD = 0;
dTotalOLD = dTotal;
strValue = "0.0252154";
dTotal = dTotal + (Double.parseDouble((String)strValue));
System.out.println(dTotalOLD + " + " + strValue + " = " + dTotal);
dTotalOLD = dTotal;
strValue = "0.0250356";
dTotal = dTotal + (Double.parseDouble((String)strValue));
System.out.println(dTotalOLD + " + " + strValue + " = " + dTotal);
System.out.println("dTotal = " + dTotal);
Actual Results =
0.0 + 0.0252154 = 0.0252154
0.0252154 + 0.0250356 = 0.050251000000000004
dTotal = 0.050251000000000004
Expected Results =
0.0 + 0.0252154 = 0.0252154
0.0252154 + 0.0250356 = 0.050251
dTotal = 0.050251
In the main application I upload a file and sum the items for validation but most of the time the total is not what I expect.
What am I doing wrong?
Mark

Answer 1

If you really absolutely need exact results, use BigDecimals.
With doubles, not even 0.1 is exactly 1/10. The IEEE double value closest to 0.1 is approximately 0.1+5.5511*10^-18 -- there is a slight, but significant difference. In calculations these "representation errors" along with others accumulate and eventually can give you relative errors of significant magnitude, although most of the time they stay under 10^-14, 10^-15