README.md

Vending machine [Adapter pattern]

Description

Module Vending machine is a simple implementation of the Adapter pattern. This is one of the most simple structural design patterns: it acts as a bridge between two incompatible interfaces.

Our office recently acquired a new vending machine. It's one of the ultimate ones and offers great products, but its buy method only admits electronic payment. We have some old-fashioned workers in the office that don't like or are not used to these technologies and stick with non-electronic payment; and the bosses are worried about for them to feel left apart. We cannot change how the office works, and they won't buy another office, this is a new expensive one.

public class VendingMachine {
    public String buy(Product product, ElectronicPayment payment) {
        // Machine operations to sell the product and claim the price.
    }
}

The receptionist, who is popular and friendly with all co-workers and whose working place is close to the vending machine, offered to act as an intermediate for the non-electronic payers. Everytime anybody come to the machine, he will ask them what type of payer they are. If it is the case of a non-electronic payer, he'll ask them for the money, whichever type it is; and then he'll make the electronic payment through the office online system for them.

So, all the receptionist has to do is to use a money converter, which is the so-called Adapter class. It acts as a «translator» or a bridge: it is an electronic payer, so it is able to pay through the office system; and it also «wraps» the non-electronic payer payment method in management to take the same amount of money when the vending machine asks for it, using the methods the vending machine is not built to understand, because it does not know how to interact with non-electronic payers. Fortunately, he understands how both parts work.

public class MoneyConverter implements ElectronicPayment {

    private NonElectronicPayment nonElectronicPayment;

    @Override
    public Boolean isChargeable(Float price) {
        // Code to adapt using for the nonElectronicPayment; calling itsmethods, if it's necessary.
    }

    @Override
    public String charge(Float price, String reason) {
        // Code to adapt for the nonElectronicPayment; calling its methods, if it's necessary.
    }
}

Subjects, technologies and contents

• Single Responsibility Principle (S from SOLID).
• Open/Closed principle (O from SOLID).