Variables of primitive types and variables of type reference to an object

There is a substantial difference between variables of type reference to an object and variables of primitive types:

• the value of a variable of type reference to object is a reference to an object, and not the object itself;
• the value of a variable of a primitive type is a value of the primitive type itself (and not the reference to a value or an object).

Example:

• Use of variables of type reference to object:

  public class Account {
    public int bal;
    public Account(int x) {
      bal = x;
    }
  }
  ...
  Account r1, r2;
  r1 = new Account(100);
  r2 = r1;
  r2.bal = 234;
  System.out.println(r1.bal); // prints 234
  

  The variables r1 and r2 contain references to objects, not objects. The assignment r2 = r1 assigns to r2 the reference to the object of type Account, not the object itself. Each successive modification to the object referenced from r2 will also be visible through r1.

  

• Use of variables of primitive types:

  int c1, c2;
  c1 = 100;
  c2 = c1;
  c2 = 234;
  System.out.println(c1); // prints 100
  

  The assignment c2 = c1 assigns the value 100 to c2. Successive modifications of c2 do not influence c1.