Chain of responsibility demonstration

Chain.java

public abstract class Chain {

    protected Chain next;

    public Chain() {
    }

    public void setNext(Chain next) {
        this.next = next;
    }

    public abstract void execute(Request request);

}

ChainA.java

public class ChainA extends Chain {

    @Override
    public void execute(Request request) {
        // any logic related to this class
        if (Request.Type.A.equals(request.getType())) {
            System.out.println("doing the task in condition A");
        } else {
            next.execute(request); // or else delegate to next chain
        }
    }

}

ChainB.java

public class ChainB extends Chain {

    @Override
    public void execute(Request request) {
        // any logic related to this class
        if (Request.Type.B.equals(request.getType())) {
            System.out.println("doing the task in condition B");
        } else {
            next.execute(request); // or else delegate to next chain
        }
    }

}

ChainC.java

public class ChainC extends Chain {

    @Override
    public void execute(Request request) {
        // any logic related to this class
        if (Request.Type.C.equals(request.getType())) {
            System.out.println("doing the task in condition C");
        } else {
            // last in the chain
            System.out.println("no one to handle your request");
        }
    }

}

CorDemo.java

public class CorDemo {

    public static void main(String[] main) {
        Chain chain = createChain();

        Request request = new Request(Request.Type.A);

        System.out.println(">>>> A");
        chain.execute(request);

        System.out.println(">>>> C");
        request.setType(Request.Type.C);
        chain.execute(request);
    }

    // it is important to build the chain correctly.
    private static Chain createChain() {
        Chain chainC = new ChainC();
        Chain chainB = new ChainB();
        Chain chainA = new ChainA();

        chainA.setNext(chainB);
        chainB.setNext(chainC);

        return chainA;
    }

}

Request.java

public class Request {

    private Type type;

    public Request(Type type) {
        this.type = type;
    }

    public void setType(Type type) {
        this.type = type;
    }

    public Type getType() {
        return type;
    }

    enum Type {
        A, B, C
    }

}