What is the difference between overloading and overriding?

Overloading: same name, different inputs

Overloading lets you use one friendly method name for related actions that take different inputs. The compiler picks the right one based on the arguments you pass. This happens in a single class.

class Calculator {
public:
    int add(int a, int b) { return a + b; }
    double add(double a, double b) { return a + b; }
    int add(int a, int b, int c) { return a + b + c; }
};

class Calculator {
    int add(int a, int b) { return a + b; }
    double add(double a, double b) { return a + b; }
    int add(int a, int b, int c) { return a + b + c; }
}

# Python has no true overloading.
# Default and variable arguments give the same effect.
class Calculator:
    def add(self, a, b, c=0):
        return a + b + c

Overriding: child replaces parent behaviour

Overriding happens across two classes linked by inheritance. The child keeps the same method name and parameters as the parent but gives its own body. At run time the program uses the child version.

class Animal {
public:
    virtual void sound() { cout << "some sound"; }
};
class Cat : public Animal {
public:
    void sound() override { cout << "meow"; }
};

Animal* a = new Cat();
a->sound();   // prints meow

class Animal {
    void sound() { System.out.println("some sound"); }
}
class Cat extends Animal {
    @Override
    void sound() { System.out.println("meow"); }
}

Animal a = new Cat();
a.sound();   // prints meow

class Animal:
    def sound(self):
        print("some sound")
class Cat(Animal):
    def sound(self):        # override
        print("meow")

a = Cat()
a.sound()   # prints meow

Quick comparison

• Where: overloading is in one class, overriding is across parent and child classes.
• Parameters: overloading needs different parameters, overriding needs the same parameters.
• Timing: overloading is resolved at compile time, overriding is resolved at run time.
• Goal: overloading adds flexible variations, overriding changes inherited behaviour.