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Switch Statements

You might be thinking, "What's wrong with a switch statement? It's a basic feature of the language!" You're right. A single switch statement is fine. But when you start seeing the same switch statement scattered across your codebase—switching on the same type code or enum—you have a smell.

If you add a new type (e.g., a new EmployeeType), you have to remember to find and update every single one of those switch statements. If you miss one, you get a bug. This violates the Open/Closed Principle: you should be able to add new types without modifying existing code.

"Most times you see a switch statement you should consider polymorphism." — Martin Fowler

Signs of the Smell​

  • You see the same switch or if-else chain in multiple places.
  • The switch is based on a type code (e.g., if (type == "MANAGER")).
  • You have to modify existing code whenever you add a new type.

Reasons of the Smell​

Procedural Thinking: It's easy to just write a list of instructions. Thinking in objects (polymorphism) takes a bit more effort upfront but pays off in flexibility.

Refactoring Recipe​

  • Replace Conditional with Polymorphism (The big one!)
  • Replace Type Code with State/Strategy
  • Replace Parameter with Explicit Methods

Replace Conditional with Polymorphism​

The goal is to move the logic for each specific type into its own class.

Before:

class Bird {
    int type;
    double getSpeed() {
        switch (type) {
            case EUROPEAN:
                return getBaseSpeed();
            case AFRICAN:
                return getBaseSpeed() - getLoadFactor();
            case NORWEGIAN_BLUE:
                return (isNailed) ? 0 : getBaseSpeed();
        }
        throw new RuntimeException("Should be unreachable");
    }
}

After:

abstract class Bird {
    abstract double getSpeed();
}

class EuropeanBird extends Bird {
    double getSpeed() { return getBaseSpeed(); }
}

class AfricanBird extends Bird {
    double getSpeed() { return getBaseSpeed() - getLoadFactor(); }
}

class NorwegianBlueBird extends Bird {
    double getSpeed() { return (isNailed) ? 0 : getBaseSpeed(); }
}

Now, adding a new bird only requires creating a new class. No existing code needs to be touched.

Replace Parameter with Explicit Methods​

If a method switches on a parameter to decide what to do, just split it into two methods.

Before:

void setValue(String name, int value) {
    if (name.equals("height")) {
        this.height = value;
    }
    if (name.equals("width")) {
        this.width = value;
    }
}

After:

void setHeight(int value) { this.height = value; }
void setWidth(int value) { this.width = value; }

References​