Arithmetic operation on primitive class variables

Question

Couldn't find an explicit description of what's happening so thought i'd bring this up to the community.

public class Temp {
static int i;
int j;
int sum = i+j;
}


public class Main{
public static void main(String[] args){

Temp obj = new Temp();
obj.i = 1;
obj.j = 2;
System.out.println(obj.sum); //returns '0'

}}

Is it because both integers i and j were empty during instantiation that the 'sum' variable is empty?

Thanks in advance!

Answer 1

Temp obj = new Temp(); // creates an instance of object type Temp

Here, data members, i, j, and sum are initialized to 0

obj.i = 1; // assigns value of Temp data member, i to 1
obj.j = 2; // assigns value of Temp data member, j to 2

Note that the value of data member sum of Temp Object obj is still 0.
To make, sum = i + j, you need to initialize it to i + j when i and j are initialized.

Simply write obj.setSum() method to set the value of sum and obj.getSum() after that to retrive the updated value of it.

public class Temp {
    static int i;
    int j;
    int sum = i+j;

    public void setSum(){
        sum = i + j;
    }
    public int getSum(){
        return sum;
    }

}


public class Main{
    public static void main(String[] args){

    Temp obj = new Temp();
    obj.i = 1;
    obj.j = 2;
    obj.setSum();
    System.out.println(obj.sum); //OR obj.getSum()

    }
}