change lapis block

@EventHandler
public void onInteract(PlayerInteractEvent e)
{
Action a = e.getAction();
if((a.equals(Action.RIGHT_CLICK_BLOCK) ||
a.equals(Action.RIGHT_CLICK_AIR)) && e.getPlayer().getInventory().getItemInHand().getType() == Material.COAL)
{
ItemStack item = new ItemStack(Material.AIR);
item.setTypeId(36);
Player player= e.getPlayer();
e.getPlayer().getLocation().getBlock().setType(Material.LAPIS_BLOCK);
Block block = e.getPlayer().getLocation().getBlock();
if(e.getPlayer().getLocation().getBlock().getType()== Material.LAPIS_BLOCK){
this.getServer().getScheduler().scheduleAsyncRepeatingTask(this, new Runnable(){
public void run(){
if(num !=-1){
if(num !=0){

}
else{
player.sendMessage("ok");
e.getPlayer().getLocation().getBlock().setType(Material.WATER);
e.getPlayer().getLocation().add(1,0,0).getBlock().setType(Material.WATER);
e.getPlayer().getLocation().add(-1,0,0).getBlock().setType(Material.WATER);
e.getPlayer().getLocation().add(0,0,1).getBlock().setType(Material.WATER);
e.getPlayer().getLocation().add(0,0,-1).getBlock().setType(Material.WATER);
e.getPlayer().getLocation().add(2,0,0).getBlock().setType(item.getType());
e.getPlayer().getLocation().add(-2,0,0).getBlock().setType(item.getType());
e.getPlayer().getLocation().add(0,0,2).getBlock().setType(item.getType());
e.getPlayer().getLocation().add(0,0,2).getBlock().setType(item.getType());
e.getPlayer().getLocation().add(1,0,1).getBlock().setType(item.getType());
e.getPlayer().getLocation().add(-1,0,1).getBlock().setType(item.getType());
e.getPlayer().getLocation().add(-1,0,-1).getBlock().setType(item.getType());
e.getPlayer().getLocation().add(1,0,-1).getBlock().setType(item.getType());

}

}
}
}, 0L, 20L);}
}



how can i change lapis block to water after 3second??

 

Your question is very similar to this one.
Check it out. Feel free to reply if you still don't know what to do.

 

thank you to say that
i made a hash map like this
public HashMap<Location, Block> hash = new HashMap<Location, Block>();
and
Block block = e.getPlayer().getLocation().getBlock();
hash.put(e.getPlayer().getLocation(), block );
but i donot know how can i use it ?