Wrappers and Autoboxing

[Pinki Roy]

 class TesterA {

  public static void main(String[] args) {

       Integer sum1 = 125; //line 1
       int sum2 =  125; //line 2

       System.out.print(sum1.equals(sum2)); //line 3
       System.out.print(sum2.equals(sum1)); //line 4
       System.out.print(sum1==sum2); //line 5
   }
}
                                                    

Why does line 4 give me compile time error where as line 3 does not give me any error.

[Swastik Dey]

sum1 is an Integer type object, and that's why it's allowing method calls. But sum2 is not any reference of any class, it's primitive type data. As you can't call any method on primitive type, this is the reason java introduces the concepts of these wrapper classes, for e.g. Integer,Double.

[Pinki Roy]

Swastik , thanks a lot for the clarification .

[Helen Ma]

As a friendly reminder, there will be a compilation error if we do this

int a  = null;

This is in one of the practice exam.

But this will work:

int a = new Integer(1);

The new Integer(1) will be unboxed and assigned to a.