Pattern matching of a poor man

Foo.java

import java.io.Serializable;

public class TwoAvgProtocol implements Serializable {
    interface MessageReceiver {
        public void onHave(double val);

        public void onAdjust(double delta);
    }

    static abstract class Message {
        protected abstract int getTag();

        public void receive(MessageReceiver receiver) {
            switch (getTag()) {
                case 1:
                    receiver.onHave(((Have)this).val);
                    break;
                case 2:
                    receiver.onAdjust(((Adjust)this).delta);
                    break;
                default:
                    assert false;
            }
        }
    }

    static class Have extends Message {
        public double val;
        public Have(double val) {
            this.val = val;
        }

        @Override
        protected int getTag() {
            return 1;
        }
    }

    static class Adjust extends Message {
        public double delta;
        public Adjust(double delta) {
            this.delta = delta;
        }

        @Override
        protected int getTag() {
            return 2;
        }
    }
}