Handling class specific behavior: polymorphism vs instanceof

I'm designing a system with different types of components, and I'm trying to decide whether to use polymorphism or instanceof checks for handling type-specific behavior. I see two possible approaches: Polymorphism Approach – Define all possible methods in a base class (even if only some subclasses override them). instanceof Approach – Only define relevant methods in specific subclasses and check types before calling them. Example with polymorphism abstract class Component { // Default implementations (may do nothing) void specialAction() {} } class GeneralComponent extends Component { // Doesn't need to override specialAction() } class SpecialComponent extends Component { @Override void specialAction() { System.out.println("Special action executed!"); } } // Usage void handleComponent(Component component) { component.specialAction(); // Will only do something if overridden } Example with instanceof In this approach, methods exist only in the relevant subclasses, and we check the type before calling them. abstract class Component {} class GeneralComponent extends Component {} class SpecialComponent extends Component { void specialAction() { System.out.println("Special action executed!"); } } // Usage void handleComponent(Component component) { if (component instanceof SpecialComponent) { ((SpecialComponent) component).specialAction(); } } I understand that excessive use of instanceof is generally discouraged, but adding methods to the base class that aren't shared among all the subclasses doesn't seems to be a good design choice either.

Mar 6, 2025 - 15:54

I'm designing a system with different types of components, and I'm trying to decide whether to use polymorphism or instanceof checks for handling type-specific behavior.

I see two possible approaches:

Polymorphism Approach – Define all possible methods in a base class (even if only some subclasses override them).
instanceof Approach – Only define relevant methods in specific subclasses and check types before calling them.

Example with polymorphism

abstract class Component {
    // Default implementations (may do nothing)
    void specialAction() {}  
}

class GeneralComponent extends Component {
    // Doesn't need to override specialAction()
}

class SpecialComponent extends Component {
    @Override
    void specialAction() {
        System.out.println("Special action executed!");
    }
}

// Usage
void handleComponent(Component component) {
    component.specialAction(); // Will only do something if overridden
}

Example with instanceof

In this approach, methods exist only in the relevant subclasses, and we check the type before calling them.

abstract class Component {}

class GeneralComponent extends Component {}

class SpecialComponent extends Component {
    void specialAction() {
        System.out.println("Special action executed!");
    }
}

// Usage
void handleComponent(Component component) {
    if (component instanceof SpecialComponent) {
        ((SpecialComponent) component).specialAction();
    }
}

I understand that excessive use of instanceof is generally discouraged, but adding methods to the base class that aren't shared among all the subclasses doesn't seems to be a good design choice either.