Answer:

You would not expect

    data.add( 44 );

to work, since it seems to be adding primitive data directly into the array of object references. This would not ordinarily work.

Autoboxing

However, the statement is correct. The Java compiler expects an object reference. So when it sees

    data.add( 44 );

it assumes that you want an object, and automatically does the equivalent of this:

    data.add( new Integer(44) );

This feature is called autoboxing and is new with Java 5.0. Unboxing works the other direction. The int inside a wrapper object is automatically extracted if an expression calls for a primitive. The following

int sum = 24 + data.get(1) ;

extracts the int in cell 1 of data and adds it to the primitive int 24.

QUESTION 19:

Would you expect the following to work?

Double value = 2.5;

double sum = value + 5.7;