Menu PrcessMenuOption method

Menu.java

private void processMenuOption(int optionEntered){
        VendingMachine vm = VendingMachine.getInstance();
        switch (optionEntered){

            case 1: System.out.println("Current Products Available");
                setMenuOptions(vm.getProducts());
                int optionSelected = displayMenu();

                vm.purchaseProduct(vm.getProducts().get(optionSelected-1),in);


                //re-display Main Menu
                setMenuOptions(itemArrayList);
                processMenuOption(displayMenu());
                break;

            case 2: vm.addProduct(new Product("Dummy",4.00,1));

                System.out.println(ProductInventory.getProductInventory().get(ProductInventory.getProductInventory().size()-1).getName());break;

            case 3:
            case 4: System.exit(0);

            default:System.out.println("default");
        }
    }

@adil - this is the getInstance Method in VendingMachine:

static VendingMachine getInstance(){
if(vm == null){
synchronized (VendingMachine.class){
vm = new VendingMachine();
}
}
return vm;
}