Boolean Object and boolean variable issue in JAVA

Question

I declare a Boolean variable. For example Boolean dataVal=null;
Now if I execute the following code segment:

if(dataVal)
    System.out.prin         


        

Answer 1

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
}

Answer 2

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 :)

Answer 3

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.

Answer 4

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

Answer 5

if(null) is not a valid expression, simple as that.

Under the hoods, the VM is using auto-boxing... so you get a NullPointerException.

Answer 6

Because dataVal is being casted to boolean using Boolean.booleanValue() which gets translated to null.booleanValue() which leads you to a NullPointerException.