// 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

*/