data-structures/java/SList/LList.java

/** Linked list implementation */
class LList<T> implements List<T> {
    private Link<T> head; // Pointer to list header
    private Link<T> tail; // Pointer to last element
    protected Link<T> curr; // Access to current element
    int cnt; // Size of list

    /** Constructors */
    LList(int size) { this(); } // Constructor -- Ignore size
    LList() {
	curr = tail = head = new Link<T>(null); // Create header
	cnt = 0;
    }

    /** Remove all elements */
    public void clear() {
	head.setNext(null); // Drop access to links
	curr = tail = head = new Link<E>(null); // Create header
	cnt = 0;
    }

    /** Insert "it" at current position */
    public void insert(T it) {
	curr.setNext(Link.get(it, curr.next())); // Get link
	if (tail == curr) tail = curr.next(); // New tail
	++cnt;
    }

    /** Append "it" to list */
    public void append(T it) {
	tail = tail.setNext(Link.get(it, null));
	++cnt;
    }

    /** Remove and return current element */
    public T remove() {
	if (curr.next() == null) return null; // Nothing to remove
	T it = curr.next().element(); // Remember value
	if (tail == curr.next()) tail = curr(); // Removed last
	Link<T> tempptr = curr.next(); // Remember link
	curr.setNext(curr.next().next()); // Remove from list
	tempptr.release(); // Release link
	--cnt; // Decrement count
	return it; // Return removed
    }

    /** Set curr at list start */
    public void moveToStart()
    { curr = head; }

    /** Set curr at list end */
    public void moveToEnd()
    { curr = tail; }

    /** Move curr one step left; no change if now at front */
    public void prev() {
	if (curr == head) return ; // No previous element
	Link<T> temp = head;
	// March down list until we find the previous element
	while (temp.next() != curr) temp = temp.next();
	curr = temp;
    }

    /** Move curr one step right; no change if now at end */
    public void next()
    { if (curr != tail) curr = curr.next(); }

    /** @return List length */
    public int length() { return cnt; }

    /** @return The position of the current element */
    public int currPos() {
	Link<T> temp = head;
	int i;
	for (i = 0; curr != temp; ++i) {
	    temp = temp.next();
	}
	return i;
    }

    /** Move down list to "pos" position */
    public void moveToPos(int pos) {
	assert(pos >= 0) && (pos <= cnt) : "Position out of range";
	curr = head;
	for (int i = 0; i < pos; ++i) curr = curr.next();
    }

    /** @return Current element value */
    public T getValue() {
	if (curr.next() == null) return null;
	return curr.next().element();
    }
}