package rac;

/**
 * This data-less concrete node in the doubly-linked circular list serves as a
 * "stop" point that defines a beginning and end of the list. This node is used
 * to enable visitor algorithms to traverse the list exactly once.  It also
 * provides direct access to both the head and tail of the list.
 * @author S. Wong
 */
public class RACStopNode extends ARACNode {
    public RACStopNode() {
        next = this;
        previous = this;
    }


    /**
    * This method will double dispatch to the stopCase() method of the supplied
    * visitor algorithm.
    * @param param A parameter for the algorithm to use.
    * @param visitor A visitor algorithm.
    * @return The return value of the algoirthm.
    */
    public Object execute(IRACVisitor visitor, Object param) {
        return visitor.stopCase(this, param);
    }

    /**
    * This node cannot be removed.   A null pointer is always returned.
    * @return null always.
    */
    public Object removeNode() {
        return null;
    }
}