I created gui that change input item to specified output item that is added to inventory. When i insert item and press button output item is added to inventory, but when i quit gui output item dissapears and change into input item.

protected void actionPerformed(GuiButton button)
{
MinecraftServer server = FMLCommonHandler.instance().getMinecraftServerInstance();
World world = server.worldServers[0];


if (button.id == 0){

if((Filamencik.getStackInSlot(0) !=null ) &&Filamencik.getStackInSlot(0).getItem() == pomaranczowyfilament.block){
if(entity instanceof EntityPlayer)((EntityPlayer)entity).inventory.addItemStackToInventory(new ItemStack(pomaranczowyMarfin.block, 1));
}

if((Filamencik.getStackInSlot(00) !=null ) &&Filamencik.getStackInSlot(00).getItem() == bialyfilament.block){
if(entity instanceof EntityPlayer)((EntityPlayer)entity).inventory.addItemStackToInventory(new ItemStack(bialymarfin.block, 1));
}

if((Filamencik.getStackInSlot(00) !=null ) &&Filamencik.getStackInSlot(00).getItem() == bialyfilament.block){
Filamencik.decrStackSize(00, 1);
}

if((Filamencik.getStackInSlot(00) !=null ) &&Filamencik.getStackInSlot(00).getItem() == pomaranczowyfilament.block){
Filamencik.decrStackSize(00, 1);
}

}


}

Version is 1.12.2

Could you write it for me because i don't know english so good and i don't understand what is wrong

I don't know what to change in code