Chain of Responsibility Design Pattern in Java: Before and after

Before

The client is responsible for stepping through the “list” of Handler objects, and determining when the request has been handled.

class Handler
{
    private static java.util.Random s_rn = new java.util.Random();
    private static int s_next = 1;
    private int m_id = s_next++;

    public boolean handle(int num)
    {
        if (s_rn.nextInt(4) != 0)
        {
            System.out.print(m_id + "-busy  ");
            return false;
        }
        System.out.println(m_id + "-handled-" + num);
        return true;
    }
}

public class ChainDemo
{
    public static void main(String[] args)
    {
        Handler[] nodes = 
        {
            new Handler(), new Handler(), new Handler(), new Handler()
        };
        for (int i = 1, j; i < 10; i++)
        {
            j = 0;
            while (!nodes[j].handle(i))
              j = (j + 1) % nodes.length;
        }
    }
}

After

The client submits each request to the “chain” abstraction and is decoupled from all subsequent processing.

class Handler
{
    private static java.util.Random s_rn = new java.util.Random();
    private static int s_next = 1;
    private int m_id = s_next++;
    private Handler m_next;

    public void add(Handler next)
    {
        if (m_next == null)
          m_next = next;
        else
          m_next.add(next);
    }
    public void wrap_around(Handler root)
    {
        if (m_next == null)
          m_next = root;
        else
          m_next.wrap_around(root);
    }
    public void handle(int num)
    {
        if (s_rn.nextInt(4) != 0)
        {
            System.out.print(m_id + "-busy  ");
            m_next.handle(num);
        }
        else
          System.out.println(m_id + "-handled-" + num);
    }
}

public class ChainDemo
{
    public static void main(String[] args)
    {
        Handler chain_root = new Handler();
        chain_root.add(new Handler());
        chain_root.add(new Handler());
        chain_root.add(new Handler());
        chain_root.wrap_around(chain);
        for (int i = 1; i < 10; i++)
          chain_root.handle(i);
    }
}