class C {
  private Object x;
  private void doSmthWithX() { 
     // some changes to x
  };
  public void doSmth() {
    doSmthWithX();
  }
}

class C {
  private Object x;
  private void doSmthWithX(Object  xx) { 
     // some changes to xx
  };
  public void doSmth() {
    doSmthWithX(x);
  }
}

class MyObj {
 private int x;
 
 public bar(int y) {
   x = foo(x,y);
 } 

 private foo(int x,y) { ... }
}

class MyObj {
  private List<Int> data;
  private double mean() {
    double mean; 
    for (int x : data) {..}
    return mean;
  }; 
}