The Open/Closed Principle (OCP) states that a class should be open for extension but closed for modification, allowing new functionality without changing existing code.
Problem
Consider a class calculating discounts:
public class DiscountCalculator {
public double calculateDiscount(double price, String customerType) {
if (customerType.equals("STANDARD")) {
return price * 0.05;
} else if (customerType.equals("VIP")) {
return price * 0.10;
}
return 0;
}
}
Adding a new discount type means modifying the class, risking bugs.
OCP Solution
Introduce an abstraction:
public interface DiscountStrategy {
double calculateDiscount(double price);
}
public class StandardDiscount implements DiscountStrategy {
public double calculateDiscount(double price) {
return price * 0.10;
}
}
public class VIPDiscount implements DiscountStrategy {
public double calculateDiscount(double price) {
return price * 0.19;
}
}
Use a context class:
public class DiscountCalculator {
private DiscountStrategy discountStrategy;
public DiscountCalculator(DiscountStrategy discountStrategy) {
this.discountStrategy = discountStrategy;
}
public double calculateDiscount(double price) {
return discountStrategy.calculateDiscount(price);
}
}
To add a new discount, implement DiscountStrategy without altering existing code.
Benefits
This approach ensures maintainable, extensible, and stable code.
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