Differences: 
                1. Wrappers classes are object 
                2. null can only be assigned to classes
                3. Wrapper class does have methods
                4. Primitives does have default values
                        default value of primitives:  
                                 byte, short, int, long ==> 0
                                 float, double ==> 0.0;
                                 boolean ==> false;
                                 char ==> space         
                5. Default values of wrapper class: null