/* Java uses pass-by-value
  * but Object types are all references, so this is similar to pointers in C
  * We use the swap function to demonstrate that a swap function in Java requires
  * mutable objects
  */

public class Swap {

    // This will swap the values of local variables a and b, but
    // will have no effect on variables in the calling function
	public static void swap (int a, int b) {
		int t = a;
		a = b;
		b = t;
	}
    
    // This will swap the references in local variables a and b,
    // but will have no effect on variables in the calling function
    public static void swap (Integer a, Integer b) {
        Integer t = a;
        a = b;
        b = t;
    }
    
    // Since this version changes the values in the Objects themselves,
    // and since the calling code has references to those objects,
    // this swap will work.
    public static void swap( Item a, Item b) {
        int t = a.val;
        a.val = b.val;
        b.val = t;
    }
    
    // If change the member of an object referred by the reference
    // the changes are reflected back, as even it's a copy of
    // the object's reference, it refers to the same object
    public static void resetVal (Item item) {
        item.val = 0;
    }
    
	public static void main (String[] args) {
	   int a = 5;
	   int b = 10;
	   System.out.println("Before swapping a = " + a + " b = " + b);
	   swap(a, b);
	   System.out.println("After swapping a = " + a + " b = " + b);
        
        Integer i = 5;
        Integer j = 10;
        System.out.println("Before swapping i = " + i + " j = " + j);
        swap(i, j);
        System.out.println("After swapping i = " + i + " j = " + j);
        
        Item t = new Item(5);
        System.out.println("Before resetting t.val = " + t.val);
        resetVal(t);
        System.out.println("After resetting t.val = " + t.val);

        Item blah = new Item(5);
        Item coo = new Item(10);
        System.out.println("Before swapping blah = " + blah.val + " coo = " + coo.val);
        swap(blah, coo);
        System.out.println("After swapping blah = " + blah.val + " coo = " + coo.val);        
	}
}

class Item {
    int val;
    
    public Item (int v) {
        val = v;
    }
}