# Java Pass by Value or Pass by Reference

* Java always passes arguments *by value*, NOT by reference.

  <br>

  ```java
  public class Main {

       public static void main(String[] args) {
            Foo f = new Foo("f");
            changeReference(f); // It won't change the reference!
            modifyReference(f); // It will modify the object that the reference variable "f" refers to!
       }

       public static void changeReference(Foo a) {
            Foo b = new Foo("b");
            a = b;
       }

       public static void modifyReference(Foo c) {
            c.setAttribute("c");
       }

  }
  ```

  \
  I will explain this in steps:

  1. Declaring a reference named `f` of type `Foo` and assign it a new object of type `Foo` with an attribute `"f"`.

     ```java
     Foo f = new Foo("f");
     ```

     <img src="https://i.stack.imgur.com/arXpP.png" alt="enter image description here" data-size="original">
  2. From the method side, a reference of type `Foo` with a name `a` is declared and it's initially assigned `null`.

     ```java
     public static void changeReference(Foo a)
     ```

     <img src="https://i.stack.imgur.com/k2LBD.png" alt="enter image description here" data-size="original">
  3. As you call the method `changeReference`, the reference `a` will be assigned the object which is passed as an argument.

     ```java
     changeReference(f);
     ```

     <img src="https://i.stack.imgur.com/1Ez74.png" alt="enter image description here" data-size="original">
  4. Declaring a reference named `b` of type `Foo` and assign it a new object of type `Foo` with an attribute `"b"`.

     ```java
     Foo b = new Foo("b");
     ```

     <img src="https://i.stack.imgur.com/Krx4N.png" alt="enter image description here" data-size="original">
  5. `a = b` makes a new assignment to the reference `a`, **not** `f`, of the object whose attribute is `"b"`.

     <img src="https://i.stack.imgur.com/rCluu.png" alt="enter image description here" data-size="original">
  6. As you call `modifyReference(Foo c)` method, a reference `c` is created and assigned the object with attribute `"f"`.

     <img src="https://i.stack.imgur.com/PRZPg.png" alt="enter image description here" data-size="original">
  7. `c.setAttribute("c");` will change the attribute of the object that reference `c` points to it, and it's the same object that reference `f` points to it.

     <img src="https://i.stack.imgur.com/H9Qsf.png" alt="enter image description here" data-size="original">

  I hope you understand now how passing objects as arguments works in Java :tada:


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