import java.awt.*;
import java.awt.event.*;
import java.util.LinkedList;
import java.util.ListIterator;

/**
   ListApplet: A demonstration of list operations using linked lists
   @author Greg Vogl
   last modified 2003-11-17
*/
public class ListApplet extends java.applet.Applet 
{

    /**
       HandleButton: An inner class to handle button actions.
    */
    public class HandleButton implements ActionListener
    {

	ListApplet app;
	TextField item;
	TextArea items;
	LinkedList list;
	ListIterator iterator;
	String operation;

	HandleButton (ListApplet app, TextField item, TextArea items, LinkedList list, ListIterator iterator, String operation)
	{
	    this.app = app;
	    this.item = item;
	    this.items = items;
	    this.operation = operation;
	    this.list = list;
	    this.iterator = iterator;
	}

      /**
        * Display list items in the text area.
        */
	public void showList() {
	    ListIterator i = list.listIterator();
	    items.append("List:\n");
	    while (i.hasNext())
		items.append(i.next().toString() + "\n");
	}

      /*
       * Handle button clicks.
       */
	public void actionPerformed(ActionEvent e)
	{
	    if (operation.equals("Add First")) {
		list.addFirst(item.getText());
	    } else if (operation.equals("Add Last")) {
		list.addLast(item.getText());
	    } else if (operation.equals("Remove First") && list.size() > 0) {
		item.setText(list.removeFirst().toString());
	    } else if (operation.equals("Remove Last") && list.size() > 0) {
		item.setText(list.removeLast().toString());
	    } else if (operation.equals("Get First") && list.size() > 0) {
		item.setText(list.getFirst().toString());
	    } else if (operation.equals("Get Last") && list.size() > 0) {
		item.setText(list.getLast().toString());
	    } else if (operation.equals("Add")) {
		iterator.add(item.getText());
	    } else if (operation.equals("Remove")) {
		iterator.remove();
	    } else if (operation.equals("Previous") && iterator.hasPrevious()) {
		item.setText(iterator.previous().toString());
	    } else if (operation.equals("Next") && iterator.hasNext()) {
		item.setText(iterator.next().toString());
	    }
	    showList();
	    app.repaint();
	}
    }

    Button addf, addl, remf, reml, getf, getl, prevB, nextB, addB, remB;
    TextField item;
    TextArea items;
    LinkedList list;
    ListIterator iterator;

    /**
      * Create a button handled by HandleButton.
      */
    public void makeButton(ListApplet app, Panel p, Button b, String text) {
	b = new Button(text);
	b.addActionListener(new HandleButton(app, item, items, list, iterator, text));
	p.add(b);
    }

	/**
        * Create the interface and linked list.
        */
    public void init() {
	setBackground(Color.white);
	setLayout(new FlowLayout());

	list = new LinkedList();
	iterator = list.listIterator();

      // list items
	Panel p1 = new Panel();
	p1.setLayout(new BorderLayout());
	p1.add(new Label("Item"), BorderLayout.NORTH);
	item = new TextField(30);
	item.setEditable(true);
	p1.add(item, BorderLayout.CENTER);
	items = new TextArea(10, 30);
	items.setEditable(false);
	p1.add(items, BorderLayout.SOUTH);
	add(p1);

      // linked list buttons
	Panel p2 = new Panel();
	p2.setLayout(new GridLayout(6,1));
	makeButton(this, p2, addf, "Add First");
	makeButton(this, p2, addl, "Add Last");
	makeButton(this, p2, remf, "Remove First");
	makeButton(this, p2, reml, "Remove Last");
	makeButton(this, p2, getf, "Get First");
	makeButton(this, p2, getl, "Get Last");
	add(p2);

      // list iterator buttons
	Panel p3 = new Panel();
	p3.setLayout(new GridLayout(4,1));
	makeButton(this, p3, prevB, "Previous");
	makeButton(this, p3, nextB, "Next");
	makeButton(this, p3, addB, "Add");
	makeButton(this, p3, remB, "Remove");
	add(p3);
    }
}