How to pass by reference in Java

// my class
class my_number {
  // public member variable
  public int number;
  // default constructor
  public my_number()
  {
    number = 1;
  }
}
// driver function
class Main{
  public static void main (String [] arguments)
  {
    // creating object
    my_number object = new my_number();
    // printing before update
    System.out.println("number = " + object.number);
    // update function called.
    update(object);
    //printing after update.
    System.out.println("number = " + object.number);
  } 
  // update function.
    public static void update( my_number obj ){ 
    // increments number variable.       
    obj.number++;  
    }
}

// driver function
class Main{
  public static void main (String [] arguments)
  {
    int number = 1;
    // printing before update.
    System.out.println("number = " + number);
    // update function returns a value.
    number = update(number);
    // printing after update.
    System.out.println("number = " + number);
  } 
  // update function
    public static int update( int number ){ 
    // increments number.       
     number++;
     return number; 
    }
}

// driver function.
class Main{
  public static void main (String [] arguments)
  {
    // single element array.
    int number[] = { 1 };
    // printing before update.
    System.out.println("number = " + number[0]);
    //update function.
    update(number);
    // printing after update.
    System.out.println("number = " + number[0]);
  } 
  // update function.
    public static void update( int number[] ){ 
    // increments the number       
     number[0]++;
    }
}