Low Level APIs

1
Low Level APIs
2
Low Level API

• Canvas isnt a type of screen
• Abstract must sub class it
• Has command and event handling behaviour
  available in the sub classes

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Low Level API

• Event Notification methods
• protected  void keyPressed(int keyCode)
            Called when a key is pressed.
• protected  void keyReleased(int keyCode)
            Called when a key is released.
• protected  void keyRepeated(int keyCode)
            Called when a key is repeated (held
  down).
• protected abstract  voidpaint(Graphics g)
            Renders the Canvas.
• protected  void pointerDragged(int x, int y)
            Called when the pointer is dragged.
• protected  void pointerPressed(int x, int y)
            Called when the pointer is pressed.
• protected  void pointerReleased(int x, int y)
            Called when the pointer is released. 
• void repaint()           Requests a repaint for
  the entire Canvas. 
• void repaint(int x, int y, int width,
  int height)           Requests a repaint for the
  specified region of the Canvas.

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Low Level API

• Field Summary
• static int DOWN Constant for the DOWN
  game action.
• static int FIRE Constant for the
  FIRE game action.
• static int GAME_A Constant for the general
  purpose "A" game action.
• static int GAME_B Constant for the general
  purpose "B" game action.
• static int GAME_C Constant for the general
  purpose "C" game action.
• static int GAME_D Constant for the general
  purpose "D" game action.
• static int KEY_NUM0 keyCode for ITU-T key
  0.
• static int KEY_NUM1 keyCode for ITU-T key
  1.
• static int KEY_NUM9 keyCode for ITU-T key
  9.
• static int KEY_POUND  keyCode for ITU-T key
  "pound" ().
• static int KEY_STAR  keyCode for ITU-T key
  "star" ().
• static int LEFT Constant for the
  LEFT game action.
• static int RIGHT
  Constant for the RIGHT game action.
• static int UP Constant for the UP
  game action. 

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Low Level API

• Graphics class supports
• Drawing filling of 2D geometric shapes
• Lines
• rectangles
• Arcs
• Text characters
• Color selection for the graphics pen
• Selection of font for text drawing
• Clipping
• Translation of the Graphics co-ordinate system

2D grid
x increasing
y increasing
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Low Level API

• Canvas objects can display images
• Offers the possibility for animating images
• Supports double buffereing
• MIDP only supports PNG image formats
• Need to implement runnable interface
• public class ThisClass extends Canvas implements
  Runnable
• Supports multithreading in a class other than one
  is already derived from class Thread
• Gives us the ability to treat our new class as a
  runnable object
• Code that controls the thread is placed in the
  run method

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Low Level API

• showNotify method
• protected void showNotify()
• The implementation calls showNotify() immediately
  prior to this Canvas being made visible on the
  display. Canvas subclasses may override this
  method to perform tasks before being shown, such
  as setting up animations, starting timers, etc.
  The default implementation of this method in
  class Canvas is empty.
• run() - Method in interface java.lang.Runnable
• When an object implementing interface Runnable is
  used to create a thread, starting the thread
  causes the object's run method to be called in
  that separately executing thread.