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.
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 :)
Because dataVal is being casted to boolean using Boolean.booleanValue() which gets translated to null.booleanValue() which leads you to a NullPointerException.
You can have a look at the specification for unboxing issues, your situation is described here section 5.1.8 Unboxing Conversion : If r is null, unboxing conversion throws a NullPointerException
That means your if ( /* Boolean object */ ) will never be unboxed into a boolean primitive type and therefore throw a NPE because you are doing an invalid if(null).
By the way, unboxing will work if you had:
final Boolean booleanTest = new Boolean (true);
if (booleanTest) {
// Do something
}
use BooleanUtils.tobolean(?), it returns false if the passed param is null
Boolean (class) != boolean (primitive type).
Java tries to get the primitive value calling dataVal.booleanValue(). Because dataVal is null, you get a null pointer exception.
if(null) is not a valid expression, simple as that.
Under the hoods, the VM is using auto-boxing... so you get a NullPointerException.
When you try to evaluate Boolean object value jvm internally call booleanValue() on that object as you assign null to that object it will throw NullPointerException
Booleanis an object, not a primitive, ergo null makes sense.