AP CSA: inheritance in Java | 现代数学启蒙

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1. Creating Superclasses and Subclasses

Inheritance allows a class to inherit properties and methods from another class. Here's a basic example:

Explanation: Dog inherits the eat() method from Animal. The main method creates an instance of Dog and calls both the inherited eat() method and its own display() method.

2. Writing Constructors for Subclasses

Constructors in subclasses can access parent class constructors using super():

Explanation: The Dog constructor calls the Animal constructor first, ensuring the superclass is initialized before the subclass.

3. Overriding Methods

Subclasses can modify inherited methods, a process known as overriding:

Explanation: Dog overrides the eat() method of Animal, changing the behavior when an instance of Dog calls eat().

4. Using Inheritance Hierarchies

Java supports creating a hierarchy of inheritance:

Explanation: This example shows a three-level hierarchy where Dog inherits methods from Mammal, and Mammal inherits from Animal.

5. Polymorphism

Polymorphism allows methods to perform differently based on the object that calls them:

Explanation: Depending on whether myAnimal references a Dog or Cat object, the sound() method behaves differently, showcasing polymorphism.

These examples provide a foundational understanding of how inheritance works in Java, demonstrating essential object-oriented programming techniques like constructors, method overriding, and polymorphism within class hierarchies.