Overriding vs. Overloading

• Overloading is having two methods with the same name but different types or number of parameters (or both). An example of overloading is the helper find method in the previous chapter's recursive implementation of binary search.

• A different return type as the sole difference between the two methods is not sufficient for overloading.

• The overloaded method is usually in the same class, but it can also be in derived classes.

• The overriding method must have the same signature as the overridden one in the super-class.

• Overriding never happens in the same class. It always happens in sub-classes.

Consider the following code snippets:

public class Animal {

  // fields and constructors not shown!

  public void makeSound() {
    System.out.println("Grrr.......");
  }

  public void makeSound(int repeat) {
    for (int i = 0; i < repeat; i++) {
      makeSound();
    }
  }
}

public class Dog extends Animal {

  @Override
  public void makeSound() {
    System.out.println("Wooof.......");
  }
}

public class Cat extends Animal {

  @Override
  public void makeSound() {
    System.out.println("Meow.......");
  }
}

Animal[] animals = new Animal[5];
animals[0] = new Animal();
animals[1] = new Dog();
animals[2] = new Cat();
animals[3] = new Cat();
animals[4] = new Dog();

for(Animal a: animals) {
  a.makeSound(2);
}

Exercise Identify examples of method overloading vs. method overriding.

Exercise Identify examples of static vs. dynamic polymorphism.