public class MyTask extends BukkitRunnable {
    private Block block;
	private Player p;

    public MyTask(Block block, Player p) {
        this.block = block;
    }

    @Override
     public void run(){
        block.setType(Material.AIR);
		ItemStack item = new ItemStack(Material.DIAMOND, 1);
		p.getInventory().addItem( { item });
     }
}