CSI 1101 Lab

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CSI 1101Lab 6 February 28, 2003

• Romelia Plesa
• rplesa_at_site.uottawa.ca

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Agenda

• Midterm discussion
• Graphical User Interface
• Assignment 5
• StopWatch Example

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Midterm Solution Question 1 (38 marks)

• Write an interface called Pair. A pair represents
  a group of two elements. The interface must
  contain the following methods
• Object getFirst()
• Object getSecond()
• void swap()
• Solution (5 marks)
• public interface Pair
• public Object getFirst()
• public Object getSecond()
• public void swap()

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Midterm Solution Question 1 (38 marks)

• (b) Write a linked-list implementation for the
  abstract data type Pair. This class, called
  LinkedPair, must implement the interface Pair and
  use the class Node below to store its elements
• class Node
• protected Object value
• protected Node next
• protected Node(Object value, Node next)
• this.value value
• this.next next
• Variables
• The class LinkedPair must have an instance
  variable called first to designate the first node
  of the linked-list. No other instance variable is
  necessary or allowed.

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Midterm Solution Question 1 (38 marks)

• Constructor
• Write a constructor with two parameters, both
  of type Object, that are used to initialize the
  first and second elements of the list.
• Methods
• Write all the necessary methods so that
  LinkedPair implements the interface Pair.
• boolean equals(Object obj)
• Override the definition of the method
  equals(Object obj) so that the method returns
  true
• if obj designates an object from a class that
  also implements the interface Pair and
• both data structures contain equivalent objects,
  in the same order.

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Midterm Solution Question 1 (38 marks)

• Solution
• public class LinkedPair
• // 2 marks
• private Node first
• // 4 marks
• public LinkedPair(Object firstValue, Object
  secondValue)
• first new Node(firstValue, new
  Node(secondValue, null))
• // 2 marks
• public Object getFirst()
• return first.value
• // 3 marks
• public Object getSecond()
• return first.next.value

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Midterm Solution Question 1 (38 marks)

• // 4 marks
• public void swap()
• first.next.next first
• first first.next
• first.next.next null
• // 5 marks
• public boolean equals(Object obj)
• if (! (obj instanceof Pair))
• return false
• Pair other (Pair) obj
• return getFirst().equals(other.getFirst())
• getSecond().equals(other.getSecond())

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Midterm Solution Question 1 (38 marks)

• c) Write an array-based implementation for the
  abstract data type Pair. This class, called
  ArrayPair, must implement the interface Pair and
  use an array to store its elements.
• Variables
• The class ArrayPair must have an instance
  variable called elements to designate an array of
  two elements. No other instance variable is
  necessary or allowed.
• Constructor
• Write a constructor with two parameters, both of
  type Object, that are used to initialize the
  first and second elements of the array.
• Methods
• Write all the necessary methods so that ArrayPair
  implements the interface Pair.
• boolean equals(Object obj)
• Override the definition of the method
  equals(Object obj) so that the method returns
  true
• i) if obj designates an object from a class
  that also implements the interface Pair and
• ii) both data structures contains equivalent
  objects, in the same order.

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Midterm Solution Question 1 (38 marks)

• c) public class ArrayPair implements Pair
• // 2 marks
• private Object elements
• // 4 marks
• public ArrayPair(Object firstValue, Object
  secondValue)
• elements new Object2
• elements0 firstValue
• elements1 secondValue
• // 2 marks
• public Object getFirst()
• return elements0
• // 2 marks
• public Object getSecond()
• return elements1

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Midterm Solution Question 1 (38 marks)

• // 3 marks
• public void swap()
• Object tmp elements0
• elements0 elements1
• elements1 tmp
• public boolean equals(Object obj)
• if (! (obj instanceof Pair))
• return false
• Pair other (Pair) obj
• return getFirst().equals(other.getFirst())
• getSecond().equals(other.getSecond())

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Midterm Solution Question 2 (18 marks)

• Create a class hierarchy to represent vehicles
• All vehicles have a weight (double)
• A car is a specialized vehicle that also has a
  number of passengers (int)
• A truck is a specialized vehicle that carries a
  certain load (double)
• A truck can load and unload its payload. Trying
  to unload more weight than the total weight of
  the payload has no effect (the method must also
  return false)
• The weight of a truck is the weight of the
  vehicle plus its payload.
• All the weights are expressed in tones.

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Midterm Solution Question 2 (18 marks)
public class Truck extends Vehicle
private double load Truck(double weight)
super(weight) void load(double
load) this.load load
boolean unload(double load) If (load gt
this.load) return false this.load -
load return true public
double getWeight() return super.getWeight()
load

• Solution
• public class Vehicle
• private double weight
• public double getWeight()
• return weight
• Vehicle(double weight)
• this.weight weight
• public class Car extends Vehicle
• private int passenger
• Car(double weight, int passenger)
• super(weight)
• this.passenger passenger
• public int getPassenger()
• return passenger

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Midterm Solution Question 2 (18 marks)

• (b) Complete the definition of the method
  calculateFees for the class Ferry below.
• The method calculateFees returns the total of all
  the fees for each vehicle in the ferry.
• the passage fee for a car is 10 per tonne plus
  5 per passenger
• the passage fee for a truck is 100 per tonne.
• class Ferry
• private Vehicle vehicles
• Ferry(Vehicle vehicles)
• this.vehicles vehicles

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Midterm Solution Question 2 (18 marks)

• (b) double calculateFees()
• // complete the method
• // 6 marks
• double total 0
• for (int i0 iltvehicles.length i)
• if (vehiclesi instanceof Truck)
• total 100 vehiclesi.getWeight()
• else if (vehiclesi instanceof Car)
• total 10 vehiclesi.getWeight()
  5((Car)vehiclesi).getPassenger()
• return total

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Midterm Solution Question 3 (18 marks)

• In the class SimpleList below, complete the code
  for the Method remove(Object obj) so that it
  removes the left most occurrence of obj in the
  list.
• public class SimpleList
• private static class Node
• private Object value
• private Node next
• Node(Object value, Node next)
• this.value value
• this.next next

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Midterm Solution Question 3 (18 marks)

• private Node first
• public void remove(Object obj)
• // special case the list is empty
• if (first null) // 2 marks
• return
• // special case obj is the first element
• if (first.value.equals(obj)) // 2 marks
• first first.next // 2 marks
• else
• // general case
• Node p first // 2 marks
• while (p.next ! null ! p.next.value.equals(obj
  )) 4 marks
• p p.next // 2 marks
• p.next p.next.next // 4 marks

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Midterm Solution Question 4 (10 marks)

• In the class ArrayList below, implement the
  method toArray(). The class ArrayList implements
  a variable size array so that an unlimited number
  of elements can be stored. The method toArray()
  returns an array that
• has the same size as the number of elements
  currently stored in the data-structure and
• contains all the same elements, in the same order.

private void increaseSize() Object tmp
elements elements new Objecttmp.length 3
/ 2 for (int i0 i lt last i)
elementsi tmpi public void add(Object
t) if (last elements.length)
increaseSize() elementslast t
last
public class ArrayList private Object
elements private int last public ArrayList(int
capacity) elements new Objectcapacity last
0 public int size() return last
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Midterm Solution Question 4 (10 marks)

• // Solution
• public Object toArray()
• Object result new Objectlast
• for (int i0 iltlast i)
• resulti elementsi
• return result

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Midterm Solution Question 5 (16 marks)

• Given the following class and interface
  definitions
• public interface I
• public int i()
• public abstract class A implements I
• protected int a 1
• public int get () return a
• public class B extends A
• private int b 2
• public int get () return b
• public int i() return a b

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Midterm Solution Question 5 (16 marks)

• a) For each of the following, indicate if the
  statements are valid or invalid.
• i) I o new B()
• o.i()
• (valid)
• I o new I()
• (invalid)
• I o new B()
• o.get()
• (invalid)
• B o new B()
• (invalid)

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Midterm Solution Question 5 (16 marks)

• b) True or false questions.
• The value 2 will be printed.
• B o null
• System.out.println(o.get())
• (false)
• ii) The value 2 will be printed.
• A o new B()
• System.out.println(o.get())
• (true)
• The value 1 will be printed.
• A o new A()
• System.out.println(o.get())
• (false)

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Midterm Solution Question 5 (16 marks)

• (c) Given the following method definition
• public static void mystery(String s)
• s "NEW"
• What should be the output produced by the
  following statements
• String x "OLD"
• mystery(x)
• System.out.println(x)
• ? prints "OLD"

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GUI(Graphical User Interface)

• Applications with GUI are ultimately based on AWT
  (Abstract Window Toolkit)
• Swing is an improved toolkit
• Packages for GUI
• jawa.awt - Contains all of the classes for
  creating user interfaces and for painting
  graphics and images
• java.awt.event - Provides interfaces and classes
  for dealing with different types of events
  fired by AWT components.

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Four categories of classes in AWT
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How to define a GUI

• Add window objects to the Grafical User Interface
  under the control of a layout manager
• Decide which events each object should handle by
  adding listeners for the event to the object
• The AWT Component Hierarchy

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Component Methods
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Window

• A Window object is a top-level window with no
  borders and no menubar. The default layout for a
  window is BorderLayout.
• Method
• void addWindowListener (WindowListener l)
• ? Adds the specified window listener to receive
  window events from this window

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Frame, Panel, Dialog

• A Frame is a top-level window with a title and a
  border.
• A Panel is the simplest container class. A panel
  provides space in which an application can attach
  any other component, such as buttons, text field
  and even other panels.
• Panel ltpanel namegt new Panel ( )
• ltpanel_namegt.add (myButton)
• A Dialog is a top-level window with a title and a
  border that is typically used to take some form
  of input from the user.
• has a parent (or a owner) window
• is automatically closed when the parent window is
  closed
• may contain most of the available UI Components

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Grid Layout

• The GridLayout class is a layout manager that
  lays out a container's components in a
  rectangular grid. The container is divided into
  equal-sized rectangles, and one component is
  placed in each rectangle.
• GridLayout()
• Creates a grid layout with a default of one
  column per component, in a single row.
• GridLayout(int rows, int cols)
• Creates a grid layout with the specified number
  of rows and columns.

X
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Border Layout

• A BorderLayout lays out a container, arranging
  and resizing its components to fit in five
  regions north, south, east, west, and center.
• Each region may contain no more than one
  component, and is identified by a corresponding
  constant NORTH, SOUTH, EAST, WEST, and CENTER
• When adding a component to a container with a
  border layout, use one of these five constants.
• For example
• Panel p new Panel()
• p.setLayout(new BorderLayout())
• p.add(new Button("OK"), BorderLayout.SOUTH)

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Button

• Class Button ? This class creates a labeled
  button.
• Button(String label)
• If an application wants to perform some action
  based on a button being pressed and released, it
  should implement ActionListener and register the
  new listener to receive events from this button,
  by calling the button's addActionListener method
• void addActionListener(ActionListener l)
• Adds the specified action listener to receive
  action events from this button (Interface
  ActionListener)
• Any ActionListener should implement the method
• void actionPerformed(ActionEvent e)
• Invoked when an action occurs.

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Label, TextField, List

• Class Label
• A Label object is a component for placing text in
  a container. A label displays a single line of
  read-only text. The text can be changed by the
  application, but a user cannot edit it directly.
• Label (String Text, int alignment)
• Constructs a new label that presents the
  specified string of text with the specified
  alignment
• Class TextField
• A TextField object is a text component that
  allows for the editing of a single line of text.
• TextField(String Text)
• Constructs a new text field initialized with the
  specified text
• Class List
• The List component presents the user with a
  scrolling list of text items
• List (int rows)
• Creates a new scrolling list initialized with the
  specified number of visible lines

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Assignment 5

• OBJECTIVES
• learn to create a simple graphical user interface
  
• furhter understanding of object-oriented
  programming
• follow the principles presented in class and the
  lecture notes 11
• The model (ShoppingCart) must be distinct from
  the user interface (view and controller).
• Therefore, no change to the class ShoppingCart,
  and related classes, is allowed.

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Assignment 5 StopWatchUI.java

• Step 1 instantiate window objects
• private Button bTime new Button("Add New
  Time")
• private Button bQuit new Button("Quit")
• private List output new List(10)
• private Dialog dTime new TimeDialog(this)

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Assignment 5 StopWatchUI.java

• Step 2 instantiate and set the layout
• setLayout(new BorderLayout())
• Panel bottom new Panel()
• bottom.setBackground(Color.white)
• bottom.setLayout(new GridLayout(1,2))

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Assignment 5 StopWatchUI.java

• Step 3 add window objects under the influence of
  the layout
• add(output, "Center")
• bottom.add(bTime)
• bottom.add(bQuit)
• add(bottom, "South")

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Assignment 5 StopWatchUI.java

• Step 4 It is necessary to tell the buttons where
  their listener
• code is located. This is done by instantiating
  listener objects
• and associating them with the buttons (The Java
  framework
• sends messages to the listener objects when the
  buttons are
• clicked)
• bTime.addActionListener (new ActionListener()
• public void actionPerformed(ActionEvent e)
• dTime.setVisible(true)
• )

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Assignment 5 StopWatchUI.java

• Step 5 a listener is needed to close the window
• addWindowListener(new WindowAdapter()
• public void windowClosing(WindowEvent e)
• System.exit(0)
• )

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What is more in A5?

• More buttons for adding new StoreItem,
  consequently, more dialog windows required, such
  as WeighDialog, UnitDialog, PreparedDialog
• Remove method
• This method should let user select the intended
  item to remove
• Solution
• highlight the intended item, using the method
  getSelectedIndex defined in List class, it
  returns the index of the selected item in this
  List object

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What is more in A5?

• We use linked list to implement ShoppingCart, so
  the physical size and logical size are always
  equal to each other, its not needed to evaluate
  if its already the MAX size of the list.
• Dont forget to update
• After adding or removing an item, update is
  required for both ShoppingCartUI(the view) and
  ShoppingCart(the model)
• the amount of Tax and the number of items should
  also be updated
• Tax amount and number of items are shown by Label
  objects
• Use setText(String str) method to assign captions
  for Label objects