calling a method and it doesn't do it's work

Question

I made 2 classes one is :

public class JavaApplication5 {
  public static void main(String[] args) {
    int y=0;
    cats catobject = new cats();
    catobject.ma(y);
    System.out.println(y);
  }
}

the other is :

class cats {

  public void ma(int x){
    x=x+9;
  }
}

it's supposed to print out 9 since the method ma should have added 9 to the integer y , but instead it prints out 0. why?

@cricket_007: you know that Integer objects are immutable, right? — Hovercraft Full Of Eels, Jul 17 '16 at 02:13
@HovercraftFullOfEels Right... `java.lang.Integer` is immutable. I only said *an* Integer object. — OneCricketeer, Jul 17 '16 at 02:19
@HovercraftFullOfEels Is this clearer? https://ideone.com/P0BjlQ — OneCricketeer, Jul 17 '16 at 03:30
@cricket_007: much. Now you're talking about changing the state of an existing object that contains an int field. Thank you. Objection removed. — Hovercraft Full Of Eels, Jul 17 '16 at 03:31

score 1 · Answer 1 · answered Jul 17 '16 at 01:52

When you pass an integer to a method in java, the method receives a copy of that integer. It does not modify the original. For more info on this see this link: http://javapapers.com/core-java/java-pass-by-value-and-pass-by-reference/

To make your code work, modify it to return an int. Like this:

public class JavaApplication5 {
  public static void main(String[] args) {
    int y=0;
    cats catobject = new cats();
    y = catobject.ma(y);
    System.out.println(y);
  }
}

class cats {
  public int ma(int x){
    return x+9;
  }
}

calling a method and it doesn't do it's work

1 Answers1