Question

I declare a Boolean variable. For example Boolean dataVal=null;

Now if I execute the following code segment:

if(dataVal)
    System.out.println("\n\NULL value in dataVal: "+dataVal);
else
    System.out.println("\n\nvalue in dataVal: "+dataVal);

I get NullPointerException. Well, I know its obvious, but I need to know the reason behind this.

Answer 1

When you evaluate the boolean value of a Boolean object Java unbox the value (autoboxing feature, since 1.5). So the real code is: dataVal.booleanValue(). Then it throws NullPointerException. With any boxed value, unboxing a null object throws this exception.

Before 1.5 you had to unbox the value by hand: if (dataVal.booleanValue()) so it was more evident (more verbose too 🙂