package GCB;
/*
    Define a linked list entry
        the entry contains two pointers
            the next entry in the list
            the prior entry in the list
        the entry also contains a pointer to the list head (not referenceable)
        setHead(h)  sets the pointer to the list head
        setNext(e)  sets link to next list entry
        getNext()   returns link to next list entry
        setPrior(e) set link to prior list entry
        getPrior()  returns link to next list entry
        clean()     removes a vestiges of being on a list
        finalize()  prints a message if a list entry is garbage collected
*/
public class ListEntry {

static final String CODE_FILE = "ListEntry";
static final int CODE_REVISION = 2;

    private Object head;                        // head of the linked list
    private ListEntry next,                     // next entry in the list
                      prior;                    // prior entry in the list

    public ListEntry() {                        // constructor for list entry
        head = null;                            // not on a linked list
        next = prior = null;                    // chain is empty
    }
    public void setHead(Object h) {head = h;}      // set the list head (for debug)
    public Object getHead(){return head;}          // get the list head
    public void setNext(ListEntry e) {next = e;}   // set the next entry in the list
    public ListEntry getNext() {return next;}      // get the next entry in the list
    public void setPrior(ListEntry e) {prior = e;} // set the prior entry in the list
    public ListEntry getPrior() {return prior;}    // get the prior entry in the list
    public void clean() {                          // clean up after removal from a list
        if(head==null) {
            System.out.println(CODE_FILE+
                               " attempt to clean a list entry that was not on a list!");
            Thread.dumpStack();
        }
        prior = next = null;
        head = null;
    }
    public void finalize() {                    // clean up before destruction of object
        if(head!=null) {
            System.out.println(CODE_FILE+
                               " attempt to release a linked list entry!");
            System.out.println(CODE_FILE+" head="+head.toString());
            System.out.println(CODE_FILE+" head="+head.getClass());
            Thread.dumpStack();
        }
    }
}