Tutorial:Alarm

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package Jam.firstalarm;

import wiki.Wiki;
import fang.*;
import java.awt.*;
import java.awt.geom.*;

/**
 * All about my game here.
 * @author Jam Jenkins
 */
public class FirstAlarm extends GameLoop
{
  private Sprite tri ;
   
  public void startGame( )
  {
       makeSprites( ) ;
       addSprites( ) ;
  }
   
  private void makeSprites( )
  {
       tri = new PolygonSprite( 3 ) ;
       tri.setScale( 0.1 ) ;
       tri.setLocation( 0.5, 0.5 ) ;
       tri.setColor( Color.RED ) ;
  }
   
  private void addSprites( )
  {
       canvas.addSprite( tri ) ;
  }    
}

Line 14: declares a Sprite instance variable that will be used to test the alarm.

Lines 16-20: the startGame method is called when the Start button is pressed the first time. In this method, you need to make and add all the sprites. Note: for multiplayer games, the number of players is only available once the startGame method is called.

Lines 22-28: helper method for constructing and placing sprites. The positions and sizes are relative to a screen which spans (0, 0) to (1, 1).

Lines 30-33: helper method for adding sprites to the canvas. Simply making a sprite does not make it visible. Sprites are only visible once they are added to the canvas within the bounds of the canvas and sized properly.

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package Jam.firstalarm;

import wiki.Wiki;
import fang.*;
import java.awt.*;
import java.awt.geom.*;

/**
 * All about my game here.
 * @author Jam Jenkins
 */
public class FirstAlarm extends GameLoop
{
   private Sprite tri ;
   
   public void startGame( )
   {
       makeSprites( ) ;
       addSprites( ) ;
       setupAlarm( 1 ) ;
   }
   
   private void makeSprites( )
   {
       tri = new PolygonSprite( 3 ) ;
       tri.setScale( 0.1 ) ;
       tri.setLocation( 0.5, 0.5 ) ;
       tri.setColor( Color.RED ) ;
   }
   
   private void addSprites( )
   {
       canvas.addSprite( tri ) ;
   }
   
   private void setupAlarm( double time )
   {
   	scheduleRelative(new MyAlarm( ), time ) ;    	
   }    

   private class MyAlarm implements Alarm
   {
   	public void alarm( )
   	{
   		tri.setVisible( false ) ;
   	}
   }  
}

Line 20: Makes the call to setupAlarm with an argument of 1 (corresponds to seconds, see below explanation of setupAlarm).

Lines 36-39: setupAlarm takes one double argument that corresponds to time. This argument is supplied to the scheduleRelative method (part of FANG). There are two ways to schedule timers; relative and absolute. scheduleRelative makes the alarm fire the specified number of seconds after the alarm is created. scheduleAbsolute makes the alarm fire the specified number of seconds after the START of the program. The first argument supplied to these functions is a new Alarm object of the type you created--in this example MyAlarm. The second is the time argument for the number of seconds as discussed above.

Lines 41-47: The creation of the class needed to create an Alarm. The Alarm class itself is an interface, meaning you cannot create objects of this type, so you must write a class of your own that implements Alarm. This class need only contain the public void alarm( ) method. Inside of alarm( ) you should place the code (or function call to code) that you want to execute when the alarm fires. In this case, we set the triangle to no longer be visible.

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   private class MyAlarm implements Alarm
   {
   	public void alarm( )
   	{
   		tri.setVisible( !tri.isVisible( ) ) ;
   		scheduleRelative( this, 1 ) ;
   	}
   }

Line 5: Here the argument supplied to setVisible is changed. Instead of just saying false to make the triangle vanish, we now want it to disappear and reappear. To do this, we first get the triangle's current visibility by calling tri.isVisible( ), which returns true if it is visible and false otherwise. The '!' is an operator that reverses the value of a boolean. So, if isVisible returns true, the ! changes it to false and vice versa. This flipped value is then passed into setVisible.

Line 6: This line schedules another alarm to happen in 1 second. The 'this' keyword is used to refer to the current object within the class executing the code. Because this code is inside the MyAlarm class, this refers to the current MyAlarm object.