Iterators on a linked list : Your LinkedList « Collections « Java Tutorial

1. Java Tutorial
2. Collections
3. Your LinkedList

class Link {
  public int iData;

  public Link next;

  public Link previous;

  public Link(int id) {
    iData = id;
  }

  public String toString() {
    return "{" + iData + "} ";
  }
}

class LinkList {
  private Link first;

  public LinkList() {
    first = null;
  }

  public Link getFirst() {
    return first;
  }

  public void setFirst(Link f) {
    first = f;
  }

  public boolean isEmpty() {
    return first == null;
  }

  public ListIterator getIterator() {
    return new ListIterator(this);
  }

  public String toString() {
    Link current = first;
    String str ="";
    while (current != null) {
      str += current.toString();
      current = current.next;
    }
    return str;
  }
}

class ListIterator {
  private Link current;

  private Link previous;

  private LinkList ourList;

  public ListIterator(LinkList list) {
    ourList = list;
    reset();
  }

  public void reset() {
    current = ourList.getFirst();
    previous = null;
  }

  public boolean atEnd() {
    return (current.next == null);
  }

  public void nextLink() {
    previous = current;
    current = current.next;
  }

  public Link getCurrent() {
    return current;
  }

  public void insertAfter(int dd) {
    Link newLink = new Link(dd);

    if (ourList.isEmpty()) {
      ourList.setFirst(newLink);
      current = newLink;
    } else {
      newLink.next = current.next;
      current.next = newLink;
      nextLink();
    }
  }

  public void insertBefore(int dd) {
    Link newLink = new Link(dd);

    if (previous == null) {
      newLink.next = ourList.getFirst();
      ourList.setFirst(newLink);
      reset();
    } else {
      newLink.next = previous.next;
      previous.next = newLink;
      current = newLink;
    }
  }

  public double deleteCurrent() {
    int value = current.iData;
    if (previous == null) {
      ourList.setFirst(current.next);
      reset();
    } else {
      previous.next = current.next;
      if (atEnd())
        reset();
      else
        current = current.next;
    }
    return value;
  }
}

public class MainClass {
  public static void main(String[] args) {
    LinkList theList = new LinkList(); 
    ListIterator iter1 = theList.getIterator();

    iter1.insertAfter(20);
    iter1.insertAfter(40);
    iter1.insertAfter(80);
    iter1.insertBefore(60);

    System.out.println(theList);

    iter1.reset();

    if (!theList.isEmpty() && !iter1.atEnd()){
      iter1.nextLink();
    }
    
    System.out.println("Returned " + iter1.getCurrent().iData);
    iter1.insertBefore(99);
    iter1.insertAfter(100);

    System.out.println(theList);
  }
}

{20} {40} {60} {80} 
Returned 40
{20} {99} {100} {40} {60} {80}