Kits Example

example.java

public enum KitType {
  MEMBER,
  VIP,
  VIPPLUS,
  MVP,
}

@EventHandler
public void onInventoryClick(InventoryClickEvent e) {
  Player p = e.getWhoClicked();
  PlayerInventory pInv = p.getInventory();
  if(e.getItem().getItemMeta().getDisplayName().equalsIgnoreCase("Member") {
    p.setInventory(fillInventory(p, KitType.MEMBER));
  }
  if(e.getItem().getItemMeta().getDisplayName().equalsIgnoreCase("VIP") {
    p.setInventory(fillInventory(p, KitType.VIP));
  }
  if(e.getItem().getItemMeta().getDisplayName().equalsIgnoreCase("VIP+") {
    p.setInventory(fillInventory(p, KitType.VIPPLUS));
  }
  if(e.getItem().getItemMeta().getDisplayName().equalsIgnoreCase("MVP") {
    p.setInventory(fillInventory(p, KitType.MVP));
  }
}

public Inventory fillInventory(Inventory inv, KitType type) {
  ItemStack helmet;
  ItemStack chestplate;
  ItemStack pants;
  ItemStack boots; 
  ItemStack sword;
  //declare special things as appropriate in the right places
  switch(type) {
    case MEMBER:
      //do stuff
      break;
    case VIP:
      //do more stuff
      break;
    default:
      //do other stuff
      break;
  }
  
  inv.addItem(helmet); // this will be null if nothing is assigned to it, so your test is to prevent that.
  inv.addItem(chestplate); 
  inv.addItem(pants); 
  inv.addItem(boots); 
  inv.addItem(sword); 
  
  return inv;
  
}