// polymorphism/ReferenceCounting.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// Cleaning up shared member objects

class Shared {
 private int refcount = 0;
 private static long counter = 0;
 private final long id = counter++;
 Shared() {
 System.out.println("Creating " + this);
 }
 public void addRef() { refcount++; }
 protected void dispose() {
 if(--refcount == 0)
 System.out.println("Disposing " + this);
 }
 @Override
 public String toString() {
 return "Shared " + id;
 }
}

class Composing {
 private Shared shared;
 private static long counter = 0;
 private final long id = counter++;
 Composing(Shared shared) {
 System.out.println("Creating " + this);
 this.shared = shared;
 this.shared.addRef();
 }
 protected void dispose() {
 System.out.println("disposing " + this);
 shared.dispose();
 }
 @Override
 public String toString() {
 return "Composing " + id;
 }
}

public class ReferenceCounting {
 public static void main(String[] args) {
 Shared shared = new Shared();
 Composing[] composing = {
 new Composing(shared),
 new Composing(shared),
 new Composing(shared),
 new Composing(shared),
 new Composing(shared)
 };
 for(Composing c : composing)
 c.dispose();
 }
}
/* Output:
Creating Shared 0
Creating Composing 0
Creating Composing 1
Creating Composing 2
Creating Composing 3
Creating Composing 4
disposing Composing 0
disposing Composing 1
disposing Composing 2
disposing Composing 3
disposing Composing 4
Disposing Shared 0
*/