Can you list and describe the main methods of implementing design patterns in code?

Main methods of implementing design patterns in Java code:

• Inheritance and polymorphism — often patterns use abstract classes or interfaces to define a common contract, and concrete implementations inherit and override methods.

• Composition — instead of inheritance, objects include other objects that implement the desired behavior (for example, the Strategy pattern).

• Use of interfaces and abstract classes — to define common methods and ensure flexibility.

• Factory methods and object creation patterns — to manage object creation through special methods or classes (for example, Factory, Builder).

• Delegation — passing calls to other objects to divide responsibilities.

Example of implementing the Strategy pattern:

interface PaymentStrategy {
    void pay(int amount);
}

class CreditCardPayment implements PaymentStrategy {
    public void pay(int amount) {
        System.out.println("Payment by credit card: " + amount);
    }
}

class PayPalPayment implements PaymentStrategy {
    public void pay(int amount) {
        System.out.println("Payment via PayPal: " + amount);
    }
}

class ShoppingCart {
    private PaymentStrategy paymentStrategy;

    public void setPaymentStrategy(PaymentStrategy strategy) {
        this.paymentStrategy = strategy;
    }

    public void checkout(int amount) {
        paymentStrategy.pay(amount);
    }
}

This approach allows changing behavior at runtime without modifying client code.