What is the best practice to modify an object passed to a method

Question

After passing an object into a method, I would like to change one of its fields. What\'s the best practice to do this task in Java?

Answer 1

Be aware of the fact that even if the object is passed as final it still can be changed. You just can't reassign the variable, which normally is desired for an (input/)output parameter.

Taking Jigar Joshis example:

public void increasePersonAgeByOneMonth(final Person p ){
  p = new Person(); //this won't work, which is ok since otherwise the parameter itself would not be changed by the next method
  p.setAge(((p.getAge()*12.0) + 1)/12.0); //ok
}