Do abstract properties violate the Liskov substitution principle?

Question

Suppose I have an abstract class like:

public abstract class Pet {
    private final String name;
    public Pet(String name) { 
        this.name = name 
    };

    public abstract boolean getsSpecialTreatment();
}

public final class Dog extends Pet {
    @Override public boolean getsSpecialTreatment() { return true; }
}

public final class Cat extends Pet {
    @Override public boolean getsSpecialTreatment() { return false; }
}

My program will treat Pets differently depending on whether the special treatment flag is set. My question is whether this counts as violating the Liskov substitution principle, which states 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 [...] without altering any of the desirable properties of that program (correctness, task performed, etc.).

Answer 1

In this case, users of those classes will probably write:

...
if (pet.getsSpecialTreatment()) {
    // special treatment
    ...
} else {
    // normal treatment
    ...
}
...

This code will work on both cases, so you would not be violating LSP. However, if you had

public class UnknownAnimal extends Pet {
    @Override public boolean getsSpecialTreatment() {
        throw new UnsupportedOperationException("Unknown species"); 
    }
}

then you would be violating LSP, because existing code will break when using UnknownAnimal instances.

Answer 2

No. Any usage of the method in the program would base subsequent decisions on the return value, just like any other method. By the very nature of the existence of the method, no program should make assumptions as to its outcome. Therefore the change in the value returned by this method should not change the properties of the program.