: Class SpaceInvaders

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SpaceInvaders
Class SpaceInvaders

java.lang.Object
  |
  +--java.awt.Component
        |
        +--java.awt.Container
              |
              +--java.awt.Panel
                    |
                    +--java.applet.Applet
                          |
                          +--SpaceInvaders.SpaceInvaders

All Implemented Interfaces:: javax.accessibility.Accessible, java.awt.event.ActionListener, java.util.EventListener, java.awt.image.ImageObserver, java.awt.event.ItemListener, java.awt.event.KeyListener, java.awt.MenuContainer, java.lang.Runnable, java.io.Serializable

public class SpaceInvaders
extends java.applet.Applet
implements java.awt.event.ActionListener, java.awt.event.ItemListener, java.awt.event.KeyListener, java.lang.Runnable

An applet simulating the popular Space Invaders video game. An initial screen asks player to specify a spaceship style and difficulty level to use in the game. A "Start game" button brings up the game screen. The difficulty level is achieved by adjusting the speed of the aliens. After each game, the same spaceship and difficulty choice menus appear along with a "Next game" button to allow continuous play without restarting the applet. Rules: Player may have up to three lasers on screen at a time. Three rows of eight aliens advance left to right, down, then right to left across the screen until player has shot them all or one of them hits the spaceship. Lasers are shot by pressing the spacebar, the spaceship can be moved right or left by arrow keys.

Since:: Java 1.1
Version:: 1.5, January 2002
Author:: Susan B. Cavanaugh
See Also:: Serialized Form

Inner classes inherited from class java.applet.Applet

java.applet.Applet.AccessibleApplet

Inner classes inherited from class java.awt.Panel

java.awt.Panel.AccessibleAWTPanel

Inner classes inherited from class java.awt.Container

java.awt.Container.AccessibleAWTContainer

Inner classes inherited from class java.awt.Component

java.awt.Component.AccessibleAWTComponent, java.awt.Component.AWTTreeLock

Field Summary

private int alienCount
          aliens remaining

private java.awt.Image[] alienImage
          alien image style array

private boolean appInit
          applet initialization flag

private int BEGINNER
          beginner game speed

private boolean clearScreen
          screen clearing flag

private int COLS
          number of columns in alien force

private java.awt.Choice diffChoices
          game difficulty choice menu

private int EXPERT
          expert game speed

private java.applet.AudioClip gameAudio
          game background music

private boolean gameOver
          game over flag

private Score gameScore
          current game score

private int height
          applet height

private java.applet.AudioClip hitAudio
          laser hitting alien sound

private int INTERMEDIATE
          intermediate game speed

private int LASERS
          maximum number of lasers allowed to fly

private java.applet.AudioClip laserShoot
          laser shooting swoosh

private java.awt.Image modShipImage
          modern spaceship image

private Alien[][] myAliens
          alien array

private Ship myShip
          the spaceship

private boolean playGame
          proceed with game flag

private int ROWS
          number of rows in alien force

private Point SCORE_POSITION
          position of score on screen

private java.awt.Image selShipImage
          spaceship image selection

private boolean setGame
          first game setup flag

private java.awt.Choice shipChoices
          spaceship choice menu

private java.applet.AudioClip shipHitAudio
          alien hitting ship sound

private java.awt.Image shipImage
          current spaceship image

private Star[] stars
          array of colored stars

private java.awt.Button startButton
          start game button

private java.awt.Image stdShipImage
          standard spaceship image

private java.lang.Thread timer
          thread that controls game speed

private int width
          applet width

private boolean youLose
          lose game flag

private java.applet.AudioClip youWinAudio
          victory gong

private Laser[] zappers
          laser array

Fields inherited from class java.applet.Applet

accessibleContext, serialVersionUID, stub

Fields inherited from class java.awt.Panel

base, nameCounter

Fields inherited from class java.awt.Container

component, containerListener, containerSerializedDataVersion, dbg, dispatcher, layoutMgr, listeningBoundsChildren, listeningChildren, maxSize, ncomponents, printing, printingThreads

Fields inherited from class java.awt.Component

actionListenerK, adjustmentListenerK, appContext, background, BOTTOM_ALIGNMENT, CENTER_ALIGNMENT, changeSupport, componentListener, componentListenerK, componentOrientation, componentSerializedDataVersion, containerListenerK, cursor, dropTarget, enabled, eventMask, focusListener, focusListenerK, font, foreground, graphicsConfig, hasFocus, hierarchyBoundsListener, hierarchyBoundsListenerK, hierarchyListener, hierarchyListenerK, incRate, inputMethodListener, inputMethodListenerK, isInc, isPacked, itemListenerK, keyListener, keyListenerK, LEFT_ALIGNMENT, locale, LOCK, metrics, minSize, mouseListener, mouseListenerK, mouseMotionListener, mouseMotionListenerK, name, nameExplicitlySet, newEventsOnly, ownedWindowK, parent, peer, peerFont, popups, prefSize, privateKey, RIGHT_ALIGNMENT, textListenerK, TOP_ALIGNMENT, valid, visible, windowClosingException, windowListenerK, x, y

Fields inherited from interface java.awt.image.ImageObserver

ABORT, ALLBITS, ERROR, FRAMEBITS, HEIGHT, PROPERTIES, SOMEBITS, WIDTH

Constructor Summary

SpaceInvaders()


Method Summary

void actionPerformed(java.awt.event.ActionEvent ae)
          Handles game start button functions including starting game audio clip.

boolean alienHitsShip(Alien alien, Ship ship)
          Determines if an alien collided with the spaceship.

java.lang.String getAppletInfo()
          Returns information about this applet.

java.lang.String[][] getParameterInfo()
          Returns information about the parameters that are settable in the HTML file.

void init()
          Initialize the game: Set black background with stars randomly distributed, load game sounds and spaceship and alien images, initialize game object locations as they will appear on screen.

void itemStateChanged(java.awt.event.ItemEvent ie)
          Handles menu selections for game difficulty and spaceship style.

void keyPressed(java.awt.event.KeyEvent ke)
          Handles a space bar press as an attempt to shoot a laser and shoots a laser only if fewer than the maximum number allowed are on screen; play shooting sound if shot was made.

void keyReleased(java.awt.event.KeyEvent ke)
          not used

void keyTyped(java.awt.event.KeyEvent ke)
          not used

boolean laserHitsAlien(Laser zap, Alien alien)
          Determines if a laser has hit an alien.

void paint(java.awt.Graphics g)
          Paint all game objects and manage the moving of aliens and lasers.

void run()
          Controls game speed by sleeping, then repainting when needed.

void start()
          Restarts game music after minimization/maximization sequence if the music had been playing, then start game motion thread.

void stop()
          Stops Space Invaders game including all audio clips.

void update(java.awt.Graphics g)
          Overrides update to eliminate clearing of the graphics context before each screen paint in order to avoid annoying flicker and clears the screen when a flag is set.

Methods inherited from class java.applet.Applet

destroy, getAccessibleContext, getAppletContext, getAudioClip, getAudioClip, getCodeBase, getDocumentBase, getImage, getImage, getLocale, getParameter, isActive, newAudioClip, play, play, resize, resize, setStub, showStatus

Methods inherited from class java.awt.Panel

, addNotify, constructComponentName

Methods inherited from class java.awt.Container

add, add, add, add, add, addContainerListener, addImpl, adjustListeningChildren, applyOrientation, checkGD, countComponents, createChildHierarchyEvents, createHierarchyEvents, deliverEvent, dispatchEventImpl, dispatchEventToSelf, doLayout, eventEnabled, findComponentAt, findComponentAt, findComponentAt, getAccessibleAt, getAccessibleChild, getAccessibleChildrenCount, getAlignmentX, getAlignmentY, getComponent, getComponentAt, getComponentAt, getComponentCount, getComponents_NoClientCode, getComponents, getInsets, getLayout, getListeners, getMaximumSize, getMinimumSize, getMouseEventTarget, getPreferredSize, getWindow, initIDs, insets, invalidate, invalidateTree, isAncestorOf, layout, lightweightPaint, lightweightPrint, list, list, locate, minimumSize, nextFocus, numListening, paintComponents, paintHeavyweightComponents, paramString, postProcessKeyEvent, postsOldMouseEvents, preferredSize, preProcessKeyEvent, print, printComponents, printHeavyweightComponents, processContainerEvent, processEvent, proxyEnableEvents, proxyRequestFocus, readObject, remove, remove, removeAll, removeContainerListener, removeNotify, setFocusOwner, setFont, setLayout, transferFocus, validate, validateTree, writeObject

Methods inherited from class java.awt.Component

action, add, addComponentListener, addFocusListener, addHierarchyBoundsListener, addHierarchyListener, addInputMethodListener, addKeyListener, addMouseListener, addMouseMotionListener, addPropertyChangeListener, addPropertyChangeListener, areInputMethodsEnabled, bounds, checkImage, checkImage, checkWindowClosingException, coalesceEvents, contains, contains, createImage, createImage, disable, disableEvents, dispatchEvent, enable, enable, enableEvents, enableInputMethods, firePropertyChange, getAccessibleIndexInParent, getAccessibleStateSet, getBackground, getBounds, getBounds, getColorModel, getComponentOrientation, getCursor, getDropTarget, getFont_NoClientCode, getFont, getFontMetrics, getForeground, getGraphics, getGraphicsConfiguration, getHeight, getInputContext, getInputMethodRequests, getLocation, getLocation, getLocationOnScreen_NoTreeLock, getLocationOnScreen, getName, getNativeContainer, getParent_NoClientCode, getParent, getPeer, getSize, getSize, getToolkit, getToolkitImpl, getTreeLock, getWidth, getWindowForObject, getX, getY, gotFocus, handleEvent, hasFocus, hide, imageUpdate, inside, isDisplayable, isDoubleBuffered, isEnabled, isEnabledImpl, isFocusTraversable, isLightweight, isOpaque, isRecursivelyVisible, isShowing, isValid, isVisible, keyDown, keyUp, list, list, list, location, lostFocus, mouseDown, mouseDrag, mouseEnter, mouseExit, mouseMove, mouseUp, move, nextFocus, paintAll, postEvent, prepareImage, prepareImage, printAll, processComponentEvent, processFocusEvent, processHierarchyBoundsEvent, processHierarchyEvent, processInputMethodEvent, processKeyEvent, processMouseEvent, processMouseMotionEvent, remove, removeComponentListener, removeFocusListener, removeHierarchyBoundsListener, removeHierarchyListener, removeInputMethodListener, removeKeyListener, removeMouseListener, removeMouseMotionListener, removePropertyChangeListener, removePropertyChangeListener, repaint, repaint, repaint, repaint, requestFocus, resetGC, reshape, setBackground, setBounds, setBounds, setComponentOrientation, setCursor, setDropTarget, setEnabled, setForeground, setLocale, setLocation, setLocation, setName, setSize, setSize, setVisible, show, show, size, toString, transferFocus

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, registerNatives, wait, wait, wait

Field Detail

SCORE_POSITION

private final Point SCORE_POSITION

position of score on screen

ROWS

private final int ROWS

number of rows in alien force

COLS

private final int COLS

number of columns in alien force

LASERS

private final int LASERS

maximum number of lasers allowed to fly

BEGINNER

private final int BEGINNER

beginner game speed

INTERMEDIATE

private final int INTERMEDIATE

intermediate game speed

EXPERT

private final int EXPERT

expert game speed

myShip

private Ship myShip

the spaceship

gameScore

private Score gameScore

current game score

width

private int width

applet width

height

private int height

applet height

zappers

private Laser[] zappers

laser array

myAliens

private Alien[][] myAliens

alien array

alienCount

private int alienCount

aliens remaining

gameAudio

private java.applet.AudioClip gameAudio

game background music

hitAudio

private java.applet.AudioClip hitAudio

laser hitting alien sound

shipHitAudio

private java.applet.AudioClip shipHitAudio

alien hitting ship sound

youWinAudio

private java.applet.AudioClip youWinAudio

victory gong

laserShoot

private java.applet.AudioClip laserShoot

laser shooting swoosh

alienImage

private java.awt.Image[] alienImage

alien image style array

shipImage

private java.awt.Image shipImage

current spaceship image

selShipImage

private java.awt.Image selShipImage

spaceship image selection

stdShipImage

private java.awt.Image stdShipImage

standard spaceship image

modShipImage

private java.awt.Image modShipImage

modern spaceship image

stars

private Star[] stars

array of colored stars

startButton

private java.awt.Button startButton

start game button

shipChoices

private java.awt.Choice shipChoices

spaceship choice menu

diffChoices

private java.awt.Choice diffChoices

game difficulty choice menu

appInit

private boolean appInit

applet initialization flag

setGame

private boolean setGame

first game setup flag

clearScreen

private boolean clearScreen

screen clearing flag

youLose

private boolean youLose

lose game flag

timer

private java.lang.Thread timer

thread that controls game speed

gameOver

private boolean gameOver

game over flag

playGame

private boolean playGame

proceed with game flag

Constructor Detail

SpaceInvaders

public SpaceInvaders()

Method Detail

init

public void init()

Initialize the game: Set black background with stars randomly distributed, load game sounds and spaceship and alien images, initialize game object locations as they will appear on screen.

Overrides:: init in class java.applet.Applet

start

public void start()

Restarts game music after minimization/maximization sequence if the music had been playing, then start game motion thread.

Overrides:: start in class java.applet.Applet

run

public void run()

Controls game speed by sleeping, then repainting when needed.

Specified by:: run in interface java.lang.Runnable

update

public void update(java.awt.Graphics g)

Overrides update to eliminate clearing of the graphics context before each screen paint in order to avoid annoying flicker and clears the screen when a flag is set.

Overrides:: update in class java.awt.Container

Parameters:: g - Graphics context to draw in.

paint

public void paint(java.awt.Graphics g)

Paint all game objects and manage the moving of aliens and lasers. Game ends when all aliens have been shot down, or one of the aliens has hit the spaceship.

Overrides:: paint in class java.awt.Container

Parameters:: g - Graphics context to draw in.

laserHitsAlien

public boolean laserHitsAlien(Laser zap,
                              Alien alien)

Determines if a laser has hit an alien. Method: Test all four corners of the laser to see if any of them falls within the alien object. Since the laser is smaller than the alien, this test is sufficient.

Parameters:: zap - the Laser object; alien - the Alien object
Returns:: laser "is within alien" flag

alienHitsShip

public boolean alienHitsShip(Alien alien,
                             Ship ship)

Determines if an alien collided with the spaceship. Method: Assumes there is a collision if alien is lower on screen than ship's nose AND alien's x coordinate is between ship's x extents.

Parameters:: alien - the Alien object; ship - the Ship object
Returns:: alien hit spaceship flag

keyPressed

public void keyPressed(java.awt.event.KeyEvent ke)

Handles a space bar press as an attempt to shoot a laser and shoots a laser only if fewer than the maximum number allowed are on screen; play shooting sound if shot was made.

Specified by:: keyPressed in interface java.awt.event.KeyListener

Parameters:: ke - KeyEvent object describing the user input

keyTyped

public void keyTyped(java.awt.event.KeyEvent ke)

not used

Specified by:: keyTyped in interface java.awt.event.KeyListener

keyReleased

public void keyReleased(java.awt.event.KeyEvent ke)