Fail to call method from Keyword

Hi all, please help me.
I create a def in keyword


def Init_Cart(int hoc_phi_goc,int giam_gia,int hoc_phi_da_giam,int ma_don_hang)


Cart cart = new Cart(hoc_phi_goc,giam_gia,hoc_phi_da_giam,ma_don_hang);

return cart;


Then I call it in a testcase
**Cart cart = CustomKeywords.‘com.kyna.util.Cart.Init_Cart’(hoc_phi_goc, giam_gia, hoc_phi_da_giam, 0)
I run testcase, but i failed because of **Test Cases/MuaHang FAILED because (of) java.lang.InstantiationException: com.kyna.util.Cart

**How should i deal with them?

please paste the entire code of your keywords.groovy. it seems to me like you are not loading cart class or the cart class itself have some error which you have to resolve