Hard to spot bugs

Submitted by pwnell on Sun, 08/02/2009 - 12:08

It took me a full 10 minutes to track down this stupid bug.  It is not intuitive.  I guess it is the penalty one pays for terseness:

          vCostEntry.getCost().put(vDBField, Utils.makeProperString(vExportToExcel).equals("DISCOUNT")?((int)Utils.getDouble(vRawAmount)):GetIntFromFormattedCurrency(vRawAmount));

Some definitions to explain above:

 

  public Map<String, Integer> getCost() {

    return mCost;

  }

and
  private Integer GetIntFromFormattedCurrency(String pFormattedAmount) {
   ... 
  }
So what is the bug? I got a NullPointerException.  Assume that Utils.makeProperString never returns null.  Assume the Map is not null. Assume in this case the ternary operator evaluated to the else clause. 
 
Here is the solution:

          vCostEntry.getCost().put(vDBField, Utils.makeProperString(vExportToExcel).equals("DISCOUNT")?(Integer)((int)Utils.getDouble(vRawAmount)):GetIntFromFormattedCurrency(vRawAmount));

 

The bug is that the types of the values in the ternary operator ?: need to be consistent with the LHS type, but was not.  In this case we tried to:

Integer <= int : Integer

which failed when GetIntFromFormattedCurrency(vRawAmount) returned a null, since Java will try to convert that to the explicit cast performed in the other part of the ternary operator - NOT very intuitive. By casting the first part of the ternary operator back to Integer, all works fine.  

 

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