package OOscheme;

/**
 * Concrete implementation of the non-empty list interface, INEList.
 * Contains two pieces of data:<ul>
 <li>first: an Object representing the first data element
 <li>rest: an IList object representing the rest of this non-emptylist.</ul>
 * When a class contains other objects that are isomorphic to itself,
 * this class is called a composite.</p>
 * Provides concrete code for <ul>
 <li>a constructor to initialize this NEList to a given first and rest,
 <li>the getFirst() method for accessing the first data element,
 <li>the getRest() method for accesssing the rest of the list,
 <li>the execute method: simply calls the nonEmptyCase method of the IListAlgo
 parameter, passing to this method itself as the host and the given input
 Object as the input.</ul>
 * Note the class is not public in order to hide from client code outside of
 * the OOscheme package.
 * @author Dung X. Nguyen
 * @since Copyright 2005 by DXN - All rights reserved
 */
public class NEList implements INEList {

    /**
     * The first data element of this NEList.
     */
    private Object _first;
    /**
     * The rest or "tail" of this NEList.
     * Data Invariant: _rest != null;
     */
    private IList _rest;

    /**
     * Initializes this NEList to a given first and rest.
     * @param first the first data element of this NEList.
     * @param tail != null, the rest of this NEList.
     */
    public NEList(Object first, IList tail) {
        _first = first;
        _rest = tail;
    }

    /**
     * Returns the first data element of this NEList.
     * This method is marked as final to prevent all subclasses from
     * overriding it.  Finalizing a method also allows the compiler to generate
     * more efficient calling code.
     */
    final public Object getFirst() {
        return _first;
    }

    /**
     * Returns the rest of this NEList.
     * This method is marked as final to prevent all subclasses from
     * overriding it.  Finalizing a method also allows the compiler to generate
     * more efficient calling code.
     */
    final public IList getRest() {
        return _rest;
    }


    /**
     * Calls the nonEmptyCase method of the IListAlgo parameter, passing to this
     * method itself as the host parameter and the given input as the input
     * parameter.
     * This method is marked as final to prevent all subclasses from
     * overriding it.  Finalizing a method also allows the compiler to generate
     * more efficient calling code.
     */
    final public Object execute(IListAlgo algo, Object... inp) {
        return algo.nonEmptyCase(this, inp);
    }
}