Homework 5: GUI Components and Data Structures

In this exercise you will create an applet with a GUI to manage a doubly linked list of strings.

1. Review Lecture 9, Lecture 10 and Lab 8. Also see the Web Resources JavaScript example list2.htm.
   
2. Create a directory named javahw5/ in your directory.
3. Create an HTML document named List.html and save into your javahw5/ directory.
   • The title of the document should be "List Applet by Your Name."
   • Create an applet tag with code ListApplet.class, width 400 and height 300.
     
4. Create a Java applet named ListApplet.java and save into your javahw5/ directory.
   • Create the class definition: class ListApplet extends java.applet.Applet
5. Create the interface by putting GUI elements in an init() method.
• Create a label Item.
• Create a text field of width 30 named item.
• Create a scrollable non-wrapping text area of width 30 and height 10 named items.
• To reduce the amount of repetitive code, create a method named makeButton().
  • Its arguments: a ListApplet, a Panel, a Button and a String.
  • It should create a new button, add an action listener, and add the button to the panel.
• Create buttons Add First, Add Last, Remove First, Remove Last, Get First, Get Last.
  • makeButton(this, panel2, addFirst, "Add First");
• Create buttons Previous, Next, Add and Remove.
  
• Add these 13 GUI elements to a layout manager.
• Group buttons by adding them to panels, then adding the panels to the applet.
• The label, text field and text area could go in a panel with BorderLayout.
• The first six buttons could go in a panel with GridLayout of 6 rows and 1 column.
• The remaining four buttons could go in a panel with GridLayout of 4 rows and 1 column.
• Each GUI element needs to be a class variable (declared outside any method).
• Import the necessary classes from java.awt and java.awt.event.
• Save changes and compile by typing javac ListApplet.java
  
• Test by opening List.html in a browser.
  
6. Create a linked list and list iterator in init().
   • The first six buttons are handled by a LinkedList object.
     • LinkedList myList = new LinkedList();
   • The other four buttons are handled by a ListIterator object.
     • ListIterator myIterator = myList.listIterator();
   • myList and myIterator should be class variables (declared outside any method).
   • Import the necessary classes from java.util.
7. Create a method named showList() to display the items in the text area.
   • Add "List:" to the text area using items.append("List:\n");
   • Create a ListIterator named i from the linked list.
   • Loop through the list items while i.hasNext() is true.
     • Add each to the text area using items.append(i.next().toString() + "\n");
8. Handle the events.
• Add an inner class named HandleButton which implements ActionListener.
• HandleButton needs six class variables and constructor arguments:
  • ListApplet, TextField, TextArea, LinkedList, ListIterator, String
  • In the constructor, set each class variable equal to its corresponding argument, e.g. this.app = app;
• All the following actions are handled using if statements in an actionPerformed() method.
• If the user clicked an Add button, an element should be added to the list.
• Add First adds an item to the beginning of the list; Add Last adds to the end.
  • myList.addFirst(item.getText());
• Add uses the ListIterator and adds the text field item at the current position.
• If the user clicked a Remove button, an element should be removed if one exists, i.e. myList.size() > 0
  • Remove First removes the item at the beginning of the list; Remove Last removes the item at the end.
    
  • Remove uses the ListIterator and removes the item at the current position.
  • Note: remove() only works after a call to previous() or next().
• If the user clicked Previous or Next, the iterator should move to the previous or next item
  • First test if a previous or next item exists, i.e. myIterator.hasPrevious()
• If the user clicked a Previous, Next, Remove or Get button, the element should also be displayed in the text field.
  • item.setText(myIterator.previous().toString());
    
• Whenever any button is clicked, call showList().
• Save, compile and test. Test the first six buttons separately from the other four.
9. Use Ark to create an archive of your directory named javahw5.zip.
10. Send javahw5.zip to the instructor as an attachment in a message with subject java hw 5.