Polymorphism Examples to Know for AP Computer Science A

Polymorphism is a key concept in AP Computer Science A, allowing methods to behave differently based on the object type. It includes method overriding, overloading, and inheritance, enabling flexible and reusable code through dynamic behavior and type safety.

1. Method overriding

   • Allows a subclass to provide a specific implementation of a method already defined in its superclass.
   • The method in the subclass must have the same name, return type, and parameters as the method in the superclass.
   • Enables dynamic method dispatch, allowing the program to determine which method to execute at runtime based on the object's actual type.

2. Method overloading

   • Occurs when multiple methods in the same class have the same name but different parameters (different type or number).
   • Provides flexibility in method usage, allowing the same operation to be performed with different types or numbers of inputs.
   • Resolved at compile-time, meaning the method to be called is determined based on the method signature.

3. Inheritance-based polymorphism

   • Achieved through class inheritance, where a subclass can be treated as an instance of its superclass.
   • Allows for code reusability and the ability to define common behaviors in a base class while allowing subclasses to implement specific behaviors.
   • Facilitates the use of polymorphic references, enabling a single variable to refer to objects of different classes.

4. Interface implementation

   • A class can implement one or more interfaces, providing concrete implementations for the methods defined in the interface.
   • Promotes a contract-based approach, ensuring that the implementing class adheres to the specified method signatures.
   • Supports multiple inheritance of type, allowing a class to inherit behaviors from multiple sources.

5. Abstract classes and methods

   • An abstract class cannot be instantiated and may contain abstract methods (methods without a body) that must be implemented by subclasses.
   • Provides a way to define a common interface while allowing subclasses to provide specific implementations.
   • Useful for defining a base class with shared functionality while enforcing certain behaviors in derived classes.

6. Dynamic method dispatch

   • The process by which a call to an overridden method is resolved at runtime rather than compile-time.
   • Ensures that the most specific version of a method is executed based on the actual object type, not the reference type.
   • Key feature of polymorphism, allowing for more flexible and dynamic code execution.

7. Upcasting and downcasting

   • Upcasting refers to treating a subclass object as an instance of its superclass, which is safe and does not require explicit casting.
   • Downcasting is the reverse process, where a superclass reference is cast back to a subclass type, which can be risky and requires explicit casting.
   • Proper use of casting is essential to avoid runtime errors and ensure type safety.

8. Polymorphic arrays and collections

   • Arrays and collections can hold objects of different classes that share a common superclass or interface.
   • Allows for the storage and manipulation of heterogeneous objects while treating them uniformly.
   • Facilitates the use of polymorphism in data structures, enabling more flexible and reusable code.

9. Runtime polymorphism vs. compile-time polymorphism

   • Runtime polymorphism (method overriding) is resolved during program execution, allowing for dynamic method selection.
   • Compile-time polymorphism (method overloading) is resolved during compilation, based on method signatures.
   • Understanding the difference is crucial for optimizing code performance and behavior.

10. The "instanceof" operator

    • Used to test whether an object is an instance of a specific class or interface.
    • Helps in determining the type of an object at runtime, which is essential for safe downcasting.
    • Enhances type safety by allowing conditional logic based on the object's actual type.