Liskov Substitution Principle

Subtypes must be substitutable for their base types.

Substitutability is a principle in object-oriented programming stating that, in a computer program, if S is a subtype of T, then objects of type T may be replaced with objects of type S

public class Bird{}
public class FlyingBird extends Bird{
    public void fly(){}
}
public class Duck extends FlyingBird{}
public class Ostrich extends Bird{}