Call by Reference

Finally, it is important to remember that any instantiated objects used as arguments to a method are passed in a call-by-reference manner. So, any modifications to those objects made inside of a method will also be reflected in the code that called the method.

Here’s a quick example:

public class Reference{
  public int x;
}

public class Main{
  public static void main(String[] args){
    Reference someRef = new Reference();
    someRef.x = 10;
    modify(someRef);
    System.out.println(someRef.x); // 15
  }

  public static void modify(Reference aRef){
    aRef.x = 15;
  }
}

As we can see, when we call the modify() function and pass a Reference object as an argument, we can modify the attributes inside of that object and see those changes back in the main() method after modify() is called.

Of course, if we reassign the argument’s variable to a new instance of Reference inside of the modify() function, then we won’t see those changes in main() because we are dealing with a newly created object.

So, we’ll need to keep this in mind as we use objects as parameters and returned values in any methods we create in our programs.