Lecture Summary 5

Applet

• Applet methods
• public void init()
• public void start()
• public void stop()
• public void destroy()
• public URL getCodeBase()
• public URL getDocumentBase()
• public AudioClip getAudioClip(URL url, String name)
• public Image getImage(URL url, String name)

Events and Listeners

• A event is an object that represents some occurance which we may want to handle.
• Often generated by user actions: keyboard, mouse, etc.
• Can also can be generated by other programs.
• There are different types of events represented by different classes: MouseEvent, ActionEvent, etc.
• A listener is an object that waits for and responses to events.
• There are different types of listeners represented by different listener interfaces: MouseListener, ActionListener, etc.
• A listener class should implement one of the listener interfaces.
• Interface MouseListener
• void mousePressed(MouseEvent event)
• void mouseReleased(MouseEvent event)
• void mouseClicked(MouseEvent event)
• void mouseEntered(MouseEvent event)
• void mouseExited(MouseEvent event)
• Class MouseEvent
• Point getPoint()
• int getX()
• int getY()
• int getClickCont()
• Example: Dots.java, DotsMouseListener.java [Dots.html]
• Interface MouseMotionListener
• void mouseMoved(MouseEvent event)
• void mouseDragged(MouseEvent event)
• Example: RubberLines.java [RubberLines.html]
• Interface KeyListener
• void keyPressed(KeyEvent event)
• void keyReleased(KeyEvent event)
• void keyTyped(KeyEvent event)
• Class KeyEvent
• int getKeyCode()
• constants for all keys
• Example: Direction.java [Direction.html]

Animation

• An animation is a constantly changing series of pictures or images that create the illusion of movement
• We can create animations in Java by changing a picture slightly over time
• The speed of a Java animation is usually controlled by a Timer object
• Timer class
• Timer(int delay, ActionListener listener)
• void addActionListener(ActionListener listener)
• boolean isRunning()
• void start()
• void stop()
• Example: Rebound.java [Rebound.html]
• This applet requires Java 2. Some browsers does not support Java 2. You can run this applet using appletviewer.

Arrays

• An array is an ordered list of values, which are of the same type. That type can be primitive types or reference types (class or interface).
• Arrays are objects. Array types are reference types.
• Arrays are of fixed size and are always bound checked.
• The length of array: ia.length
• Index starts from 0. An array of size N is indexed from 0 to N-1
• Examples:

int[] ia = new int[3];
ia[0] = 1; ia[1] = 2; ia[2] = 3;

int ia[] = new int[3];
ia[0] = 1; ia[1] = 2; ia[2] = 3;

int[] ia = { 1, 2, 3};

float[][] mat = new float[4][4];

for (int y = 0; y < mat.length; y++) {
  for (int x = 0; x < mat[y].length; x++)
    mat[y][x] = 0.0;
}
 

• Array as parameters
• An entire array can be passed to a method as a parameter
• Like any other object, the reference to the array is passed, making the formal and actual parameters aliases of each other
• Changing an array element in the method changes the original
• Arrays of objects
• The elements of an array can be object references
• The following declaration reserves space to store 25 references to String objects


     String[] words = new String[25];
 

• It does NOT create the String objects themselves
• Each object stored in an array must be instantiated separately
• Example: GradeRange.java
• Command line arguments
• public static void main(String[] args)
• Example CommandLineArguments.java
• Output:
C:\Courses\CSC224\Examples>java CommandLineArguments
args.length=0

C:\Courses\CSC224\Examples>java CommandLineArguments Hello World!
args.length=2
args[0]=Hello
args[1]=World!

• Example: CD.java, CDCollection.java, Tunes.java

Sorting

• Selection sort, insertion sort
• A utility class: Sorts.java
• Example: SortGrades.java
• Sorting arrays of objects
• Example: SortPhoneList.java, Contact.java

Vector Class

• A varaible-sized list of objects.
• Methods:
• void addElement(Object obj)
• void insertElementAt(Object obj, int i)
• void setElementAt(Object obj, int i)
• Object remove(int i)
• boolean removeElement(Object obj)
• void removeElementAt(int i)
• void clear()
• boolean contains(Object obj)
• int indexOf(Object obj)
• Object elementAt(int i)
• boolean isEmpty()
• int size()
• Examples: Beatles.java