Đa hình (Polymorphism)
 Ví dụ
class Animal {
  public void animalSound() {
    System.out.println("The animal makes a sound");
  }
}
class Cat extends Animal {
  public void animalSound() {
    System.out.println("The cat says: meow!");
  }
}
class Dog extends Animal {
  public void animalSound() {
    System.out.println("The dog says: woof!");
  }
}
class Cow extends Animal {
  public void animalSound() {
    System.out.println("The cow says: moo!");
  }
}
class Main {
  public static void main(String[] args) {
    Animal myAnimal = new Animal();  // Create a Animal object
    Animal myCat = new Cat();  // Create a Cat object
    Animal myDog = new Dog();  // Create a Dog object
    Animal myCow = new Cow();  // Create a Cow object
    myAnimal.animalSound();
    myCat.animalSound();
    myDog.animalSound();
    myCow.animalSound();
  }
}
  
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