创建Double以测试null检查时引发的null指针异常

Question

This may be a stupid question, but I have a method that will convert Doubles or BigDecimals to a formatted String:

//There is also a method that accepts BigDecimals
public String convertToCurrencyString(Double aAmount) {
    if(aAmount == null){
        return "$0.00";
    }
    NumberFormat numFormat = DecimalFormat.getCurrencyInstance(Locale.US);
    numFormat.setMinimumFractionDigits(2);
    String amount = numFormat.format(aAmount);
    return amount;
}

I'm currently trying to test this method with JUnit by instantiating a Double:

Double nullDouble = new Double(null);

The problem is a NullPointerException is being thrown when the creating the Double. Is there a way to stop this happening, or is this normal behaviour? The need for the null check is that there are some older records in a database that have these Doubles and BigDecimals set to null

Answer 1

new Double(null) calls the Double(String) constructor, which tries to parse the given string into a double. But with a null String it fails with a NullPointerException.

The proper way to pass a null Double to your method is to simply call:

String resultForNull = convertToCurrencyString(null);

Also since your method does not use the enclosing class' state, it may make sense to make it static .