Hello, (java noob warning)
I was reading about generics(works like templates in c++) and decided to write a generic LinkedArray Class (I plan to use this not only for bullets but particles and enemies).
import java.util.ArrayList;
/**
*
*/
/**
* @author Anya
*
*/
public class LinkedArray<T>
{
private ArrayList<T> elements = new ArrayList<T>();
private int size;
private int freeElements = 0;
private int activeElements = 0;
private int[] freeElementIndex;
public LinkedArray( int size, T e )
{
this.size = size;
this.activeElements = 0;
this.freeElements = size;
this.freeElementIndex = new int[size];
elements.ensureCapacity(size);
for( int i = 0; i < size; i++ )
{
elements.add(e);
}
for( int i = 0; i < size; i++ )
{
freeElementIndex[i] = i;
}
}
public int getSize()
{
return size;
}
public int getActiveElements()
{
return activeElements;
}
public void add( T e )
{
if( freeElements == 0 )
{
return;
}
freeElements--;
int index = freeElementIndex[freeElements];
elements.set( index, e );
activeElements++;
}
void remove( int index )
{
freeElementIndex[freeElements] = index;
freeElements++;
activeElements--;
}
public T get( int index )
{
return elements.get( index );
}
}
And here’s how it is used…
/**
*
* @author Richard Eric M. Lope (Relminator)
* @version 1.00 2013/3/04
*/
import java.awt.Graphics2D;
public class BulletFactory
{
private LinkedArray<Bullet> bullets;
public BulletFactory( int size )
{
Bullet b = new Bullet();
bullets = new LinkedArray<Bullet>( size, b );
}
public int getSize()
{
return bullets.getSize();
}
public int getActiveBullets()
{
return bullets.getActiveElements();
}
public void addBullet( Bullet bullet )
{
bullets.add( bullet );
}
void removeBullet( int index )
{
bullets.remove( index );
}
public void updateBullets()
{
for( int i = 0; i < bullets.getSize(); i++ )
{
Bullet b = bullets.get(i);
if( bullets.get(i).isActive() )
{
b.update();
if( (b.position.x < 0) || (b.position.x > Globals.SCREEN_WIDTH) ||
(b.position.y < 0) || (b.position.y > Globals.SCREEN_HEIGHT) )
{
b.kill() ;
bullets.remove(i);
}
}
}
}
public void renderBullets( Screen screen, Graphics2D g, ImageAtlas imageAtlas )
{
for( int i = 0; i < bullets.getSize(); i++ )
{
Bullet b = bullets.get(i);
if( b.isActive() )
{
int frame = b.getFrame();
g.drawImage( imageAtlas.getSprite(frame),
(int)b.position.x - imageAtlas.getSprite(frame).getWidth()/2,
(int)b.position.y - imageAtlas.getSprite(frame).getHeight()/2,
screen );
}
}
}
}
My questions are:
-
Why does updateBullets() and renderBullets() work? Since I made a local copy of the bullet b from bullets.get(index). Does Bullet b and bullets.get(i) share the same reference and is “deep-copied”?
*Note that I did that code out of curiosity and crossed my fingers it works. -
Why can’t I use normal arrays (vs arrayList ) when doing generic classes?
Thanks!
